I have done similar stuff to this and I use Removable Magic Tape. You can, if you look hard enough see where the tape was/is, on the film, but a bit of shading on the paper as you expose, eliminates any trace of the tape.
It is a Scotch product and goes under the moniker 811.
Comes in two sizes small and large diameter cores for the small and large dispensers, both sizes I have are 1/2" wide.
The beauty of this product is that it pulls off easily and most importantly doesn't really leave a residue on your film.
As a side benefit, this tape is really good for lifting dust from a neg without doing damage to the emulsion. I've been using this tape for many years.