With the slider out, the switch is "on" all the time. Depending on the keyboard this could cause it to not respond. Clears have the tightest stems for some reason. I always cycle caps on and off a loose Clear before mounting them if they're going onto Clears on a board so they won't be too hard to remove later.
If you can get the top cover off you can just put the slider back and put the top back on. You may have to desolder the switch, though, if the plate doesn't allow the switch top to be removed.