Custom taillight issues.

I have tried searching for a way to make custom tail lights like so many of you do. By this I mean like using a vent as the headlights basic shape and then adding in other lighting to make it look totally unique. My issue always arises where once I have got it sized properly and set it in place, sometimes my computer will momentarily lag and then the part is not where I would like it to be. Then once I try to grab the smaller light innside the larger vent it always tries grabbing the vent instead of the light ( if that makes sense? )
Do any of you guys have any tips besides a better computer
my funds are currently more focused on getting my built 02 wrx back on the road. Thanks.
Jordan.
Do any of you guys have any tips besides a better computer

Jordan.