Automatically merge cells and Vertical Text

[Excel New]

Hello,
I am currently working on an ATTENDANCE SHEET for a class.
In this particular attendance sheet, the cells E11 to AC11 have 3 options for input:
1 - Regular Class Session (attendance is recorded)
H - Holiday (attendance is not recorded)
CS - Class Suspension (attendance is not recorded)

What I would like to happen is if I input H or CS,
the cells intended for marking attendance of the day (rows 15 to 37)
would be automatically look like merged into one cell so that instead of putting their attendance,
I will just input the name of holiday (if the input is H) or reason for suspension (if the input is CS). [like in the picture].

Please note that the rows from 15 to 37 of columns E to AC have specific border designs, data validation or formulas.
I prefer to have them back if I remove/change the input CS or H.

And I intend to manually input the name of holiday or reason for class suspension.

I just need the rows to automatically look like one cell (like MERGE IN CENTER & VERTICAL TEXT) if the input is either H or CS.

Thank you so much in advance for the help.

 

[Excel New]

If there is a way to avoid merging the cells, I'd prefer that because it secures the formatting and formulas inserted on the cells.