Don't drill or weld your rops.
I've mounted lights and other things many ways... real tempo stuff was with a magnetic base... have also done quick and dirty attatchments as well as decent looking ones with hose clamps. Heavier stuff with U bolts, like the factory does for the canopies. Have also used those spring loaded 'hand clamps' i call them.. they are used to clamp tow flats together to dry, or hold something, etc.. they are nice and strong.. I'm holding up a radion in the barn with one right now.. clamp is holding on a 2x6, and the open arms are holding the bracket to a little boom box for tunes while i work on the tractors..
For farly permanent but easy to remove attatchments, why not make a small lshaped bracket, attatch it to the rops via ubolt, or hose clamp, then make the light mount to it with a wingnut or similar.. hav ethe power on a quick release insulated plug / jack.. run the wires in wireloom or 'spagetti' tubbing, lashed to the uprights and routed to power... use zip ties to hold the wire loom in place.
Good luck.
Soundguy