Been on BME and although I originally only thought of having one tongue piercing, i've decided i really want 2 centre ones... but is this possible in the same day or is it best advised to space them out
No, not two on the same day. I doubt any reputable piercer would even do that for you anyway. It takes about 3 weeks for the initial swelling to go down and that's when you get a changeover bar put it. Twice the swelling will mean twice the time and will most probably cause a higher risk than it already carries.
No offence but i've read up on the risks such as losing the enamel on your teeth and chipping them and as long as they are properly placed and possibly use PTFE instead of metal once downsizing then the risk should be significantly reduced. As for going into one hole... i wouldnt have them done too close to each other anyway.
yeah well that's what my mate thought, but now she's risking losing her front teeth, but whatever. i guess you must be getting them placed pretty far back to resist the temptation of running them between your teeth, as that's what everyone i know who's had it done does.