I'm not suggesting removing the "checkbox" for Replace in Selection. Merely adding a new button, [In Selection]

I find the checkbox not as easy to use as a button, depending on how you are doing your search/replaces.
Frequently it winds up I need to check the box, do the replace + select more text, do a replace, etc. Close Dialog.

When you use Replace again, the option will need to be unchecked. Further, when the option "replace in selection" is checked, if there are no Search matches within the current selection - you can't even do a find next (or replace)...

One additional note, (which I dont recall if I mentioned before or not)... The Replace dialog is missing the Find dialog's option "Move to Start/End". Some other editors implement this feature as an option "[x] Don't Wrap Around"