Ah, ha! Thanks, Italo, that really helped!
1) I had read over the "Naming…" section several times, but it seemed to apply more to newly created presets rather than tweaks to a factory one. I now know better.
2) Your original suggestion to go from -50db to 0 did not work for me. In fact, I couldn't even get a minor volume pedal swell to work. BUT…I thought, well, if that makes it worse, what would happen if I went the other way, say to -80db? Bingo! Now I can swell into this effect, and can further adjust it if need be.
3) I still find that the (tweaked) #325 is louder than other presets. Can that also be adjusted, like in outgain? Whatever the proper procedure, can that also be saved in the tweaked version of #325 (please specify how; this is something essential)?