Well, not easily.
Marking what code should be live-updated is not live_call's only function - it is also what runs the actual (new) code, subsequently backing out before running the original code if it did. So it cannot "automagically" apply to everything as it cannot have any effect on compilation process to inject that line.
You could add in a live_call to all scripts automatically one or other way (probably find-replace-in-files file-start "^" via any external code editor via regular expression), but there are a few gotchas:
- GMS1 tends to freak out if project files are being changed while also open in it, sometimes to the point of overwriting changes on save/compile or corrupting the file/project entirely. In other words, if using GMS1, make sure that the project isn't open in it while you do large external changes.
- If your project is really big, I expect the thing to not work that well - GMLive's server is watching specified files rather than directories as whole, so having way too many files might add up.
Generally I'd suggest to add live_call as a snippet to GameMaker (there's snippets.txt) for quick insertion and to add it to multiple potential subjects of interest before running the game.