Your question is overly broad and there are way too many variables for a concise answer. You need to open the Help files and type Grace Notes. I can't find the 25 Mac manual online anymore but here's the page to start with for 26.

https://usermanuals.finalemusic.com/FinaleMac/Content/Finale/Grace_notes.htm?Highlight=grace%20notes

Happy to answer more detailed questions once we know what you're trying to do.

Let me be clear about the Help files. They used to be online so that I could give a link to a page or even quote it. Apparently, that is not the case except for 26.

I'm hoping it's a glitch and not permanent. This page gives you the ability to download folders containing the HTML for the pages. The 25 folder is over 2GB — I downloaded it before I gave my earlier answer.

https://makemusic.zendesk.com/hc/en-us/sections/115002894667-User-Manuals

Pretty sure there's little difference between 25 and 26 as far as grace notes are concerned. Working a huge project that needs to be delivered tomorrow. Not being able to find the link to help files online is world class annoying. Anyway, I hope it's just a server down.