Hi Can I use unbreakable gel on cotton lace to make a lace?

I don't quite understand what you mean.  Do you want to make a stiff edible lace? Or what exactly is unbreakable lace?

You can, but test it first to make sure the gel isn't going to stick to the lace. You could also make a copy of the lace so that you have a picture of it that's flat, then put it under a piece of waxed paper and pipe the gel over that, using the lace photo as a template. Depending on what kind of gel you're using it may or may not stick to the paper and it might shrink as it dries, too, so test it out first.