Is their any paperwork on this transaction? If so, it should address questions like this. Generally speaking, child support orders can only be changed by a court.
Also, it is unlikely that you can sign over guardianship in Texas (the terms you are using do not make sense), so I'm not sure exactly what you mean. If you clarify your question, maybe we can have a more helpful answer.
Child support has to paid according to the terms of the order that created the child support obligation. The child support order says to pay a certain amount on each certain date to a certain person. So yes, child support keeps going to the other parent even though that parent no longer has the child.
The obligor (or the person ordered to pay child support) can file a motion to modify and say that child support should go to the grandparents. I'm not sure about the terms of this temporary guardianship, so I'm not sure if that suggestion makes sense in your context.
It would be a wise investment to go consult with a local family law attorney who knows the Dallas courts and who can ask you all the questions necessary to give you better advice. I'm very familiar with the courts in Dallas and know that they take child support very seriously, so please consult with an attorney to make sure you completely understand all your rights, options, and obligations before taking any other actions.