Filling micro cracks in painted plaster?

[Pesco]

Micro-weaving would have been good, but it doesn't exist. Can you fill minimally small cracks with something and paint over? Plaster and caulk are too thick. Looks like thin pencil lines in a few places in the room.

 

[lajsiiwan]

You should be able to smear some white grout over it and paint on it. Don't forget that the grout should preferably be paintable

Edit: Strike that, I read too poorly. It should be possible to just paint over if it's so thin that even grout doesn't go in.