I haven’t done this myself, but I think I have enough understanding of the DCS Updater to answer this.
I once had trouble with installing my dad’s DCS modules on a pc where the registry items of my DCS modukes were apparently interfering and we had to delete those.
First, you might want to de-activate your modules on Steam. (I’m not sure if this is actually required but it may prevent the kind of trouble I mentioned earlier)
Then you just install the standalone DCS World, it should ask you if you want to install your modukes when you open the module manager.
You say yes, and either then or after restarting it will ask you to enter your keys.
Now you will see your number of activations left going down to 9,8,7 or something like that, but don’t worry: you essentially have infinite activations. After they run out, you will get a new activation after a month.
If something goes wrong and you still need to install a module but the module manager doesn’t prompt you anymore, look up “DCS Updater install repair revert” and you will find an ED Forums thread by Skatezilla that shows how you can tell the Updater directly to install a module.
Steam and the stand-alone use the same location, as in X:/Users/(you)/Saved Games/DCS. Where it differs is what version you install, i.e. stand-alone does make a DCS.Alpha and DCS.beta separate save locations I believe.