Regex to change multiple lines

[Termoregolato]

Il 03/09/20 16:10, Termoregolato wrote:

> I need to change every occurrence of a sequence between two chars

Thanks to all for your replies, it's time to learn regular expressions, 
but now I've some valid pointers from you.

The work I must do here, to explain, is to get some markdown files, and 
add the strikethrough in a different color from the original, so I've do 
a bit of confusion between markdown "~~" and my "%%" in examples, where 
I wanted to reduce the number of lines.