creating the style is easy, changing the text from one style to another is harder to do commandline. Is it possible just to change textstyle1 to the properties that you want? If not, the best way would be to use a lisp statement to select all of the text that is style textstyle1, then you can use the CHANGE command to change the style.
For the arrowheads, I would cover all of your bases for different ways that the dimensions could be set up and set DIMBLK, DIMBLK1, and DIMBLK2 to your arrow block, then do a DIM UPDATE ALL