i'm interested to know, say if i got hired as a s/o on a 767 does that mean i stay with that aircraft through the rest of career or would i'd be able to switch to an A330 or 747, and do i have to have captain status to be able to switch or'upgrade' so to speak

It's all about senority. At my company, you can change planes any time you want if you are moving up in status: the size/pay of the aircraft OR seat (FO to Captain). If you want to bid down in pay or seat they won't let you until you've been in that position two years. They paid a lot for your training and want to get their monies worth.

If you were hired as a SO (the 767 doesn't have them), then you can bid any plane you want as FO and get it when you can get it senority wise. When you want to be a CA bid it, and you get it when your senority will hold it.

At my company we have three pay types: small (737-300/500/700), medium (737-800/900, 757-200/300), and large (767-200/400, 777-200). Then we have First Officer pay and Captain pay. Normally, you'd be hired as a 737 FO getting a mix of small and medium pay. You then could bid 757/767 and get a mix of medium and wide pay. If you bid the 777, your pay would be all large. Then you could upgrade first to the 737, getting a mix again, but at Captain pay. Theoretically, you could be hired as a 737 FO and then fly the 757/767 and 777 all the same year. You'd be in training all year, but it could happen. I did my 737, 757/767 types all in one year.

Companies are different, so you'd have to see one each one's policy is.