Don't complicate it.

According to what you said, you have filed status transfer petition from F2 to F1 based on the I20 you received from school A. Once your petition is approved, you are on F1 you don't have to file another one.

When you get the I20 from school B, keep it. If you decide to go to school B. You can transfer from school A to school B before you register. This is an easy process to be done by the ISO of school A. You need to tell them your intention before you registered. Take both I20s to report to school B.

Make sure you only register in one school, and your name is on SEVIS with correct school. It's critical if you are really studying at this school while you have I20 issued by this school and your name on SEVIS is associated with this school. This important after 911. Any other questions, you should consult your ISO.

Getting visa from US consulate to change your status is not a really good idea if you are not traveling out of North America.