Painting Text on Model
You don't provide any dimensions or sizes, but...

Assuming that the text is sufficiently elevated from the rest of the model, you could use a firm solid (as opposed to soft and spongey) roller, of an appropriate width.

This should enable you to paint just the text without getting paint on the rest of the model.


If the text is small and in a "valley" or groove, then a narrow roller would be required, in order to avoid the surface either side of the text.
If the text is not on a flat, or smooth surface, then a small diameter roller might be required.
If you can't find a tiny paint roller, you could jerry-rig one using a paper clip and a roller wheel from an old cassette tape