Words have typical meanings and then they have legal meanings, you can look at the details of the first conviction under the law and draw conclusions about the threshold for "stirring up hatred":
https://www.report-it.org.uk/three_men_convicted_in_first_pr...
It is very clear to me that the Scottish courts regard stirring up hatred to mean a specific threat of violence but YMMV.
If you don't have anything nice to say, don't say anything at all. Now with the force of law.