Hmmm......It's been decades since I've grown watermelon and I might not know what I'm talking about.........but with some other plants, it seems like a plausible idea to cut some of the vines back. I don't know if leaving a fresh cut would expose the plant to more pests/diseases though. Surely more people might weigh in here who know more than I. But.....if you already have fruit growing, I wonder if cutting the vines back will just stimulate more leaf growth and actually take away from the already-growing fruit. ?? Sorry I couldn't be of more help. If no one else adds to this, maybe you could Google for answers?

I've never trimmed my WM vines but if you have the room to allow them to spread then perhaps just removing any new melons (rather than trimming the foliage) would give you the desired results.

Trimming foliage is never really in the interest of the strength of the plant. But, as noted, trimming off any new melons would concentrate fruit growth and maturation in the ones that remain.

Occasionally, I've pinched just the growing tips - maybe 2 inches or so - from rampant winter squash vines, but that was to head them back and encourage branching.

I Answered in your other post.