Lock following cells form user input and colour the same with grey.

Hello!

The below mentioned description enumerates my problems and requesting your valued expertise for its subsequent solution:

With regards to attendance:

Cells E2 and so on are the ordinal dates.
The below cells have a drop down list.
Would like to restrict/lock all the cells below from user input if "S" is entered in any cell
in the 3rd row. Plus if the cells below could be coloured grey.(it would be best of all the cells below could be replicated with "S" as well)

With regards to score-sheet:
Cell F16 to O16 depicts question numbers.
Would like to restrict/lock all the following cells from G17 to O17 from user input,based on the value "Ab" entered in F17 and to be darkened by grey colour.
Same goes for G18 to O18 based on the value "Ab" entered in cell F18 and so on till the 10th candidate i.e. cells from G26 to O26
should be locked based on the value "Ab" entered in F26.
Would like to repeat the above for the forth coming sets of tests and so on (T17:AC26, AH17:AQ26 and so on, so forth).

An excel file has been attached for our convenience.
Thanks and regards