Exclusive Arm Recording...

or use alt+click on rec arm button

This will work for selecting a single track by double clicking on the track, such as on the track number area. It won't work for multiple tracks. The previous keyboard shortcut will. Import this cycle action as before. Go to Reaper Preferences - Mouse Modifiers Context: Track Control Panel

alt-click on rec button, a good way to go, thanks!

Thanks for all the suggestions guys! I'll try these methods out, but given how many years I've been using exclusive arming, I'm guessing that I'll go to set up mics to record something new, forget about using modifiers and just go and click the new track's record button, because it's right there... Is there a way to maybe defeat the initial function of single clicking the record button and arming non-exclusively, so I can avoid making the mistake?

After 6 years of toughing it out, I'm so tired of having to undo accidentally mangled audio from previously recorded tracks I've forgotten to disarm. (Yes, I know about Alt+Click, but I have not been able to get used to using a keyboard modifier to interact with a UI button by default) Is there STILL no way of changing the DEFAULT record arm behavior to be exclusive?! (I do NOT want every track I select to arm for recording!) I just want to switch the default left click of the record arm button with the alt+click behavior.

Posted this in the feature requests forum: Also created a video demonstrating why this feature is needed:

It doesn't look like you can change the mouse modifiers for the record arm button like you want, but I've had this same problem and here's how I solved it: I created a custom action that goes like this: Track: Unarm all tracks for recording Track: Toggle record arm for selected tracks and assigned that to "r". Whenever I want to record arm a bunch of tracks, I just select all of them and hit "r". Those tracks and *only* those tracks get record armed. Anything that wasn't selected is disarmed. Maybe that will work for you too.