Delete multiple lines by specifying their line numbers in Notepad++

You metionded to delete/remove specific non-consecutive lines regardless of their contents.

For these special lines in my opinion a regular expression or function makes sense only when you need to repeat this very often.

From comments above bookmarking by manually using Ctrl + G and Ctrl+F2 in combination is my recommendation too.

So you can quickly mark some lines by repeating the key sequence Ctrl+G, linenumber, Enter and Ctrl+F2 with the existing functionality.

Of course, for multiple use with the same lines, a macro can be recorded and executed.

As a further option, you should nevertheless use the functions on the Ctrl+M tab (e.g. Regular expression, Bookmark line, ...) for your needs.