03 Check Engine Light Question

[TouchdownTN]

I have a 03 H2 with 60,000 miles. Onstar told me that it was due to a emissions problem. They told me to drive it a highway speed and the light may go off. They told me it shouldn't damage the truck and if the light did not go off to of course stop by my Hummer dealer which is 60 miles away and not open on my days off. Last night the light would flash then go back solid again then flash then go back solid. I haven't noticed the light flashing today, my question is am I doing any damage to my truck or is it ok to take my truck to a local mechanic and get them to turn off the check engine light with their programmer? Thanks for the help!