Can you link the exact board you have? I think you mean "HHKB layout" because an HHKB uses topre switches, and not MX as shown in your photo.
The term for the original keycap is an "off-center 6u spacebar" Yes, you can find them around.
I'm going to say that yes, you can move that switch. To check, pull up a program to test keystrokes like EK switchhitter. Then, use a paperclip to touch the positive and negative pads on the center switch position. If it registers a keypress, you know you're good to move it.