PLEASE READ BEFORE SOLVING:

1. Each Across clue in this grid can be solved only after an additional instruction is applied to the wordplay component. 

2. The instruction that needs to be applied to the clues can be found as the solution to 4D

3. Each half of the instruction in 4D applies to roughly half of the across clues

5. All down clues are normal cryptic clues and don't use the additional instructions