you will have to make two changes:
1) Change the days of the week listed across the top row
2) change the formulas in every cell where the day number is shown (this is "harder" part)
to change 1) simple type in the new day names
To change 2) you need to make changes to the following items:
1) The main calendar
2) the previous month calendar
3) the next month calendar
For the Main calendar:
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update the day names in row 1
update the formulas as follows:
A2=Month and Year::$A$4+DURATION(0, 1− Month and Year::$A$5+ (7×(ROW()−2)÷2+COLUMN()))
this is shorthand for... select cell A2, then type (or copy and paste from here) the formula:
=Month and Year::$A$4+DURATION(0, 1− Month and Year::$A$5+ (7×(ROW()−2)÷2+COLUMN()))
hit the return key. select cell A2, copy
select row 2, paste
select row A, copy
select row 4, now hold the command key and select rows 6, 8, 10, and 12
paste
For the previous month calendar:
update the first letter for the day of the week in row 2
now update the formulas in row 3 as follows:
A3=Month and Year::$A$8+DURATION(0,COLUMN()− Month and Year::$A$9+1)
select A3, copy,
select A3 thru G3, paste
For the next month calendar:
update the first letter for the day of the week in row 2
A3=Month and Year::$A$12+DURATION(0,COLUMN()− Month and Year::$A$13+1)
select A3, copy,
select A3 thru G3, paste
now save this as a template using the menu item "File > Save As Template..."