Experiment with the following:
Case 1:To delete lines containing the text string “yourword”
Find what zone: (?-is)^.*?\Qyourword\E.*?\R
Replace with zone: Make sure this zone is empty!
Search mode: Regular expression
To delete the last 4 (for example) characters from each line:
Find what zone: (?-s).{4}$
Replace with zone: Make sure this zone is empty!
Search mode: Regular expression
Note: A line must have at least 4 characters on it to be affected!