Hi, and welcome to the forum.

You need to be a bit clearer about item 7.
How many rows do you want to leave before repeating steps 1-6? Simply saying in another 10-30 rows isn't very clear.

Then is it a consistent gap between the rows you want to operate on, or does this vary and you need to work out which is the first row in the next 'block'? In which case what's the rule?

Finally how many iterations do you need to make? Is this determined by the number of rows, or a fixed number.

Rgds