Maybe I didn't explain it right or not understand what you want to do. My understanding is that you want to click on an image in the contact sheet and tag it rather than select it. If you have 3000 images but only want 100 tagged, that's 100 clicks not 3000. If that's correct, you can select multiple images by Ctrl-clicking (Windows) each image, that's just one click per selected image or 100 Ctrl-clicks to select 100 images. Then with 100 images selected, Ctrl-+ and the 100 images selected will all be tagged. The only thing this adds to your request, as I understand it, is the Ctrl-+ to tag the selected images.