Would you like to try and modify it yourself?
Tip: Make a leader, then run the code below (just paste into command-line) & select it. make a change to the leader manually and re-run the code below and again select it. Press F2 to display all the DXF codes. Compare the 2 to check what has changed.(entget (car (entsel)))
I prefer using some decent text editor which allows comparison. Something like NotePad+ should do as it shows 2 files next to each other highlighting differences.
First, I can see that the 141 code governs the offset. Then the 291 code governs if the background is turned on / off. The 292 code governs if the background uses a blank-out or a colour. Changing the colour sets the 91 code, though this seems to be saved in RGB format.
Just be careful, as you've seen there's more than one of the same codes. E.g. the 1st 292 code is the blank-out on background, but the 2nd is the text frame. So rather than using the subst (which substitutes all items in the list matching an example) - it might be preferable to recreate the DXF list by stepping through it and only changing those which apply.
Then next to allow for asking for a offset, do somthing similar to what I did for the ON/OFF idea. Only this time use a getdist instead of a getkword.
