after 40 yrs of marriage/still married/can I use my maiden name as middle name /without paperwork

I am not familiar with Texas law specifically, but I learned in law school that you can use any name you want, without paperwork, as long as you are not using for fraudulent purposes, for example trying to fool creditors.  Of course, some people you deal with will not accept any unofficial name.  For example, if you apply for a passport, you may need proof of your official name.