Silver and gold sharpies seem to work well for the most part... I've just plucked strads with a awl for the cover taper marks. The others wipping twine though a section and tied with a square knot or saftey pins, or knitting needles (second hand shop sells them for 0.25$ for singles or a buck for a pair).
The white out seems to be a good idea, and I wouldnt worry about the chemical much just be sure to cut the white out (see the pun?)
Marking cover strands for tapering seems putsy and I'm going to try just marking point T, then counting and plucking for the taper. Point T (and R) can easily be marked with a piece of thread run through just the cover, though I do like the idea of using white out. I also have done a quick stitch, wrap (or two) and knot some thread where points T and 2 need to be held together, instead of taping them. I have always cut and pulled the thread before completing the splice, but wonder if that's necessary. That thread should get buried, and can't see how it would hurt the splice.