If you changed your passport and they put a new visa page in they will still know you already were in all that time. They will probably see you in their computer database when they swipe your visa page again. So if you have already been in 6 months you shouldn't (but your mileage will vary as always) be able to get in without being rejected at PF at the airport. If you overstay your tourist visa then you must wait 6 months + the amount of days you overstayed and probably a buffer of at least a week to make sure you got the numbers right before entering. It's 180 days MAX with a legal extension from the first day you entered in, but if you overstayed you have to take that time in to account, or so I've been previously been instructed by PF. Not sure what they do for people that over stay for years or months beyond.

A visa or passport is just a receipt record, everything these days is electronic anyways. If it was that easy to cheat the system a lot more people would do it that way. What's the trouble with the student visa? They usually process those visas in a timely manor if you have all the required docs in order.