There are some rules, but it's not really that much:

For both:

1) Pick a human/Sentient creature pair.

2) Pair first develops dreams, then mental connection and matter transport, (then magic if with unicorn,) then the transformation (stronger the internal magic, the faster the transformation), and then portals. Low magic equestrain partners will take on more human characteristics than high magic ones.

3) Have fun!

For canon stories:

1) PM me, wille179, if you want to write a canon story. I'll work with you to help keep the details straight.

2) Any crossovers need to be coordinated between the respective authors.

3) Try to pay attention to what the other canon authors are doing (i.e. read their stories) so that you know what might impact your characters.

For non-canon stories.

1) This is the only rule. Pretty much anything goes.

Woo, rules! Now I know just what the fuck I am doing.

I love you.