General modification principles.
Most modules have a big, usually blue, capacitor in the order of 0.22uF /250V to 0.68uF/250V to drop the incoming power which is then rectified and stabilized to usually -12 or -15V. X10 was invented in England so they use of course positive logical ground! In the case of MEGA32 there are two capacitors in parallel. Change it to half of the original value (MEGA32 both of them) and 400 or 600V.
Most modules uses a 10-22 Ohm 1/2W resistor in series with this capacitor in order to reduce the current when turning on power to the module. Change this one to twice the value and twice the power. In most case it will work fine without this modification but it could increase the MTBF (Mean Time Between Failure).
Some modules like the WS467 have a voltage divider consisting of two capacitors. The value of the second smaller one, going to logical ground, should not be changed. You should instead replace it with the same value and with a 400-600V type. In the case of WS467, this is the 0.1uF. The first and bigger capacitor should be changed to half of the value but 400- 600V. This capacitor is also usually blue.
Almost all modules uses a serial capacitor to insulate the receive/ transmit circuit from the main supply and to adapt the impedance to the electrical power network. It is very difficult to tell what is the actual impedance of your electrical network (your antenna!) at 120 kHz . It will change with whatever you turn on or plug in and even your cable types might affect it. However, statistically and from a practical point of view, consider it to be twice as high on 220V as on 110V if you have the same power (kW) consumption. Therefore, change this receive/ transmit capacitor to 400-600V and just to be able to physically fit it at the same place, half of the value. As I said, we can consider the impedance of the electrical network to be twice as high on a 220V supply than on 110V supply so we have not really introduced any losses. Even this one is usually also blue.
If you would need to tune/test X10 receivers or transmitters without connecting them to the mains supply, you could use a resistor of 10-15 Ohm (4.7-6.8 Ohm on 110V) to simulate an average "antenna" impedance.
Most modules use a 330k resistor coming from the incoming supply to two diodes to generate the zero crossing pulse. This value is not very critical. However due to the voltage across this resistor I recommend a physically bigger resistor like a 330k-560k 1/2W.
If the module has a triac with a voltage rating of less than 400V change it to 400V or better 600V. If it has a 400V triac, use a MOV to protect the triac. Even on modules with 600V triacs I recommend it. Note that this triac, in most cases, must have an insulated tab. See the modification of the WS467 for some sample triac data.
Appliance modules uses a "stepping relay" with a cam and a 110V coil. One should normally rewind this coil to 220V. Perhaps some trick with resistors or capacitors might work if there is physical space. I have not tried it. In fact I have not modified any appliance modules because they had plenty of 220V versions in stock here. I believe that the so called universal module also uses this principle
If you have 240V supply voltage, you have to drop away 130V to get 110V over the coil in the appliance module. If you would use a 100 Ohm resistor you would have, 130 squared, divided by 100 (16900/100)/2 = 84.5 Watts over the resistor! Divided by two, because halwave is used. However, normally a short pulse is applied to the coil so this is not continuous power.
Leonard Simms in New Zealand (lgs@midland.co.nz) reported that he has successfully modified appliance modules by using a 100 Ohm/1Watt resistor in series with the coil. My first thought was to use a 5-10W resistor instead but after thinking a little bit, I believe he is right! Perhaps a 2W resistor would be a good compromise.
If you would have some electronic failure like a blown thyristor, you would have continuous power and perhaps twice the power I mentioned above, because the blown thyristor would now supply fullwave AC, over both the coil and the resistor. A 1-2W resistor would probably just explode if it happens and probably do less damage than a 10W resistor which would heat up a lot more before it burns out.
Be careful, this could cause a fire risk. Also the optimum value or the resistor could be different between different type of modules. Some experimenting is needed. If you have a lot of patience, rewind the coil instead.
BTW, even in the States, you can buy 220V (heavy duty) appliance modules. They apparently use them for 220V water heaters and such but they do have American plugs and outlets. Also those 220V outlets are not normal US standard so standard adapters can not be used. :-(
US Standard plug Grounded plug 15A/220V plug 20A/220V plug
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O O O Ground
It is however very easy to change at least the output on such a module to accept a US standard plug. The contacts inside the are universal to accept both 15A and 20A and will work quite OK also with US standard plug. However, the plastic in the cover plate is covering some areas of the contact. Just open the module and examine the cover plate. You will find they have used a universal mold for this part and only removed some areas where they wanted to add plastic. There are clear marks how to cut the cover plate for all three types of plugs. I don't recomend cutting away the plastic without opening the module. It is too easy to get some plastic pieces in some unwanted areas. It will be a little bit hard to push in the connector but it works quite good.
If a module has a MOV, change the voltage. If it does not, add one. See the chapter about choosing components.
Another possibility is to use a 220V-110V step down transformer and add a capacitor of around 0.1uF/600V across input output so the 120 kHz can be transfered. Capacitor should be polyester, MKT or similar and 400V unit would work. However, I prefer good safety margins. This a sollution you could use on something like a CP290, TW523 minicontrollers and other units that don't drive a load. If you would use this on an lamp or appliance module, you would obviously need 110V lamps or appliances! Well, you could also put a second transformer at the output to step up the 110V to 220V but some lamp modules will not like the inductive load of the transformer. Unfortunately, this is both a little bit clumsy and slighly expensive.
Something like this:
In 220V --------o-------,|||
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0.1uF
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600V
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Out 110V --------o-------)||| Transformer
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Common 0V ----------------'|||