Stuck Kips rod retaining screw

Just rebuilt the top end on my '92 KDX200 (FMF Fatty, FMF Turbine Core, 45/155 1173 jetting, air box mod, fresh carb) and the job went off very smoothly except for one thing. The Kips rod retaining screw was so tight, I couldn't budge it without stripping the head. I am referring to the SCREW and not the Shaft Retaining NUT. Upon insp., the KIPS valves were fairly clean and operating smoothly already, so I decided to leave them in place, and continue with the rebuild. I did, however, work a bunch of carb cleaner through the valves, rinsed thoroughly, and relubed everything. I put it all back together with new Wiseco Piston/rings, gaskets, and it kicked right over on the second try. After several warm up cycles, I got it out an ran it like a top for an hour. Question is - When I go to clean the KIPS next time, how, will I get this screw out (and the rod retainer) to complete the job? Can this be drilled out then extracted easily? Should I simply clean next time with the cleaner and not disassemble if the valves are not to dirty? Eventually this will have to be tackled.
Thanks for any advice.

Thanks

I appreciate the info. - I think as long as they work smoothly, and the gears look good I may keep cleaning as prescribed (leaving them in) until I finally have take on this %$*#@ Retaining Screw. Worst case I will probably have to drill and back out with an extractor.

Clarity

Thanks, Wibby, for clearing this up for C.D. As an update also, I just spoke J.F. @ FRP, and he said this is very common problem. He hits the center of the threads with a center tap and then turns it on an angle and hits it again at a counterclockwise direction to free the screw. Sounds like you must plan on replacing the screw either way. He also added that eventually it will have to come out for full cleaning/servicing of the valves, and that cleaning w/out removal doesn't really get all the grime.