This stuff, which you might already have, is good for keeping points.
You can leave it on a brush and it will dry and keep the point well. Just swish it in water next time you use it to get rid of any residue.
What I meant was cutting the brush bristles shorter and maintaining the sharp point, to result in a shorter brush.

Ah sorry, I get you now! I have done that too but it does tend to ruin brushes that taper to a very fine point, as you said.
My metallics only brush was trimmed and reshaped several times over the years. The base of the brush shows how much it was trimmed. It went in the trash this morning, not enough left to trim.
It had been trimmed with my best parts nippers. The God-Hand’s or Zoukei-Mura being the best of the lot and Xuron’s being marginal for doing this in my experience. I don’t know if that would work very well with a very slender bristle paint brush like your asking about.
This 0/10 brush has used for applying liquid cement, putty, super glue accelerator and paint work for many years. It somehow got super glue in it and that royally jacked up the tip.
Super glue debonder gel worked pretty well stripping old paint and of course dried super glue out of this old brush saving it. Took three ten minute soaks.
It still paints well enough to suit me doing attached tools.
HTH
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