Once the template is placed against the lace side and in the right position (You can hold the template in place with a couple of bits of tape.), its simply a case of using a makeup pencil and drawing around the outline of the template.
Then you remove the template and follow the line with your blade, pressing firmly enough to slice the lace, but not so firmly you're coming through the other side and cutting the hairs.

There will always be a few casualties with the hair, but in the scheme of things, these won't matter at all.