Digital BW, The Print

You will lose nothing by re-assigning a profile to it. However, it is
up to you to keep track of what profile it really is. (One year from
now, will you remember?)  :-)

Also, PNG as I recall is limited to 8 bits per pixel component.
(Someone please correct me if I'm wrong.) That's why I don't recommend it.

I still recommend saving your master files as 16-bit TIFFs or PSDs. In
the former case, enable ZIP compression to save space.

Gigabytes are cheap these days (about a quarter per gig). Certainly
less than 1 mL of ink. Maybe consider another hard drive!  :-)

Eric