Replacing just the bolt isn't all that hard on a used saddle. Chances are, if the leather on the saddle is stretched such that you've needed to increase tension, it should be reasonably tricky, but doable.
I've done an old, super worn B5N and then another, non-Brooks which was super thick and dried. The latter took some screwdriver leverage and got a bit scuffed up.
I did it "freehand" on those, but if I had the project again, I would try mounting the saddle on a post, then clamping the post with some V-d wood into a good bench vise.
hope that helps,
- Jim
--
Jim Edgar
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