Re: have you ever added weight to a fly reel...
I only have experience adding weight to one reel; an old Pflueger 1495. It will take a lot of #3 shot in the center part of the spool; it's actually designed to do that and has an opening in the spool to insert the shot. I use it on an old solid fiberglass rod; which is plenty heavy.
Other that that, I've tried adding weight to reels in other ways (sticky-back lead wound around the spool shaft, plastic-coated metal core line, etc.), but in the end, I usually purchase a reel that works better with the rod. In my opinion, too much messing around with gear usually leads to problems.