There should be no alteration required. If you are new to bikes than you may ask few electricians first, to have some idea.
I am not a pindi resident but XANDAU (metal beam + Glass) should easily be available at any good spare parts shop.
Second thing you might need to check if GS-150 plastic case can be fitted as I am not sure. Or you need to check for other available cases.
If you do not want to get into above, you may install Honda 70 headlight that comes with CD-70 89 model and also point model of CG-125. You can simply ask for Honda 88-89 model headlight case (without meter fitting wala) and XANDAU light (beam + glass). Total cost would be around 600- 700. 500-550 ki light milay ge aur case 100-150 ka. It will bolt on fit. Reference k lye see the pic below,
