Picking everything out wasn't as bad as I anticipated. Music helped. The base cloth is a sturdy, service weight damask, not too vintage, so it can take a little punishment without falling apart.
But..web research is telling me I am well and truly screwed for using an indelible (hello!) metallic gold ballpoint ink to so arrogantly lay out the lettering. Such chutzpah!
The solution I'm too familiar with is laying in a needle-turned patch of the same base material with the tiniest, most invisible, made by blind Bavarian nuns, stitching and then, getting the damn words right, bless you Beatles.
Relax baby, it's gonna be OK.