allow all seceding citizens to move to seceded Texas, allow Puerto Rico to join the Union, and not change the flag.

If people want to secede from the Union, let them. If people want to join the Union, let them. This solves both problems. Texas is a large state, so the thousands of people that want to secede can go there, and we can allow the state to secede. Anyone in Texas who wants to remain in the Union will be allowed to move to another state. At the same time, we should welcome Puerto Rico with open arms. As an extra added bonus, we won't have to change our flag!