Yes. That info was unintentionally left out of the data file info docs. I have an
update document I'm doing for GCA5 that includes it, so that will be corrected at some point.
What you want to target is
SKCAT:category.
For example,
gives(+1 to SKCAT:book) would grant +1 per level to all skills that fall into the category
book. Likewise,
gives(=+1 to SKCAT:athletic) would grant a fixed +1 to all
athletic skills.
ETA: If you find yourself doing a bonus to multiple categories at once, look up Compound Bonuses in the
Data File Reference Guide to avoid possible issues with traits in multiple categories getting multiple bonuses.