Patching arrows with tails

[temnix]

I'm of a mind to give semi-transparent trails to arrows and bolts as they zip to the target. Indicating superspeed. That's probably not realistic, but then, in real life the arrow is sticking out of the target pretty much the moment you let go of the bowstring. Arrows don't head for anyplace. Regardless, this is the code I'm trying. It's supposed to look at single-target projectiles that use the ARARROW animation and, if there is nothing in the First trailing animation field already, enter there the name of my custom VVC.

 COPY_EXISTING_REGEXP GLOB ~.*\.PRO~ ~override~

PATCH_IF (SOURCE_SIZE > 172) THEN BEGIN

READ_SHORT 0x8 type   <- A 2-byte field

PATCH_IF type = 2 THEN BEGIN

READ_ASCII 0x104 animation  <- 8 bytes
READ_ASCII 0x136 trail1  <- 8 bytes

PATCH_IF (~%animation%~ STRING_EQUAL_CASE ~ARARROW~) & (~%trail1%~ STRING_EQUAL_CASE ~None~) THEN BEGIN

WRITE_ASCII 0x136 ~ARTAIL_#~

END
END
END

BUT_ONLY

Well, there are no errors, but nothing ends up changed. How come?