Dumb question...
Can I switch a toilet and tub in my master bath? I know the piping is different dimensions. How can I work around this?

You can't really work around this isuue, the toilet needs a 4" drain and the tub is no where near that size. You'd need to open your floor and repipe the drain lines. No small task for many DIY but it can be done. Make a drawing and send it back. Tom Speedball1 will likely read your post and provide some specs for you to follow.