Uploading new sketch to Leonardo-type boards when you've changed the HID mode
From Sparkfun's page Pro Micro Hook-upGuide

When a Pro Micro is externally reset (by pulling the RST pin low), it’ll only briefly (&lt;750ms) start the bootloader before continuing on to the sketch. If you need the bootloader to run longer, resetting twice quickly will get the Pro Micro to enter bootloader mode for eight seconds.

Hope that helps! If not there are some other procedures you might want to look into.