I live in Missouri and changed my first name and gender through the courts with a lawyer. My wife was worried about the marriage recognition, too. Despite Missouri not allowing same sex marriage, according to my lawyer our marriage is a contract that cannot be broken with such changes. It remains intact. I will either have to get it amended with my new first name (won't try the gender amendment just yet...

), or show my court order every time I get a new job and apply for spousal benefits, for instance. I go to court next Monday to try and get my name changed on my children's birth certificates.
As for the 401k/pension, my spouse is automatically my beneficiary, according to the plan my work offers. I specifically list her, too, but the last couple 401k and pension plans said if I didn't designate otherwise (and she has to sign to allow other designation) then the spouse remains the primary.
Having said all of that, you should still consult a legal representative from Texas to be sure, and contact your HR/Benefits dept. regarding the 401k.
Hope this info helps!
-Ainsley