How to change the names of Months in a calendar without breaking it?

I'm using the Google Sheets Annual Calendar template and I want to be able to change the names of the months for a tabletop thing, but doing so breaks the entire thing. I can't find another year calendar template spreadsheet that's this well-organized and all on one page.

The function each square in the calendar uses is this;

=IF(E4<>"",E4+1,IF(WEEKDAY(DATEVALUE($Z$1&$B$2&1))=5,1,""))

Or something similar.

I just want to change the real month names into some silly fantasy variants to make stuff easier to track, but nothing comes up on google for "Year calendar that does not use scripts" or anything of the sort that I can actually use. Is there an easy way to just, I dunno, change what's displayed in the field without changing the actual variable (in this case, the month's name) or something?