Change the forum ID number for the forum here f=?

not breaking, but each threads posted in each forum is attached to the forumID they are in... you would have to have a code that also change that detail... (and the database is "auto-increment", that means it would give a higher number to the next forum you create anyway, breaking your order again)

having them in order is always possible inside the forum manager itself, check this:

Admin CP+>> Forums & Moderators >> Forum Manager

at the right side of each forum you have a field with a number, and you see on top of the list that the field is named "Display Order" ... you simply have to change the number for each forum, ordering them the way you want...