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.

Small size is 21200 19243 bar code number.

Large size is 21200 69151 bar code number.