Is this legal or illegal in Texas? Flashing helmet lights on the back of your helmet with blinker/brake lights? Link below of the product

STEEL MATE Wireless Helmet Brake Light and Running Light for Motorcycle Safety Rechargeable LED Signal Light for Helmet (H2)

 

Each state has it's own regulations on what modifications can be made to a helmet. I would contact them directly. Most regulations have to do with how far out they protrude from the surface where it would materially affect it's ability to protect your head in an accident. IMO, I doubt that anyone is going to say anything so long as the lights are not blue.