Replace items "Treat as List" are displayed in two boxes, one for Search and the other for Replace, when you enter text separated by commas they are displayed in a block of text that is difficult to see and modify.
If the box where you enter text were resizable, and also if when you are in list mode there was a box that when checked would allow to show all the elements of the lists showing one for each line, it would greatly facilitate its use even when visually formatted in the commas would detect errors that are sometimes difficult to locate,
The text field is a simple text based area. There are no plans to add separate fields for list items.
You can however make the text field full screen (F10).
Unfortunately no.
ReReplacer (for Joomla 4) uses Code Mirror for the fields, so you have some line numbering and code coloring and such. That doesn't support resizing the field.
Possibly with CodeMirror, an interesting option would be, Autoresize that would allow to show more content than the current 8 lines, limited to about 15 lines maximum, as shown in "This is CodeMirror" box,
Well, the issue is more with Joomla's support for the editor field.
Joomla doesn't offer the option to pass something like a 'resizable' flag on to the editor settings. So that is the limitation here.
So again, no, I cannot give you what you are asking for at this moment.