Adapting aging view to your camera is straighforward once you understood what's going on. If you adjust the finder-image to be virtually at infinity you shouldn't have any problems when you lost the ability to adapt for closer objects but still have a sharp view at far objects.
Every finder with a fixed arrangement presents its image at some virtual distance which is calculated as 1 divided by the dioptrien-value of the finder in meters. With Nikon the picture is virtually in a distance of 1 m (finder is -1 dioptrien 1/1 = 1) with later Bronicas it is 0,67 m (-1.5 diotprien, 1/1.5 = 0,67). If you buy a correction-lens it will indicate the resulting power of the whole finder, not its actual power as a single lens (exceptions may exist, I have yet to encounter them).
Example: If you have a correction-lens inscribed "-0,5", it will produce an image when used with the finder in a virtual distance of two meters 1/0.5 = 2.
(This will probably be a sufficient correction for most older guys, it certainly is for me.)
This lens alone will have an optical power of +8.5 dioptrien when measuerd if it's for a Bronica.
If you get yourself the common "0"-correction lens for Nikon it will produce a picture virtually at infinity with the finder (1/0 = error

), but the lens itself has a power of +1.
Now you also know how to use your prescription: Look up the dioptrien-value of your finder in the manual and counteract it with a prescription to get the finder-image "zeroed in" for an image at infinity.