Setting TAL string var in inspect

[SRSeedBurners]

STRUCT SOME^MSG^DEF
STRUCT HEADER
..
STRING LENGTH[0:4]

I have a string which is buried in an struct off in the ext memory:
INT .EXT SMSG^DEF(SOME^MSG^DEF)

ptype SMSG^DEF.HEADER.LENGTH
type = STRING [0:4]

print SMSG^DEF.HEADER.LENGTH
$4 = "00688"

I'm trying to modify this value to a different length for testing.

set *SMSG^DEF.HEADER.LENGTH = "00588"
evaluation of this expression requires the program to have a function "malloc". DLL with malloc symbol should be loaded (Example: symbol $system.sys00.zcredll)

We are using Microsoft Visual Studio to cross-compile this on our windows machine. Not quite sure how to do what it's telling us.

set SMSG^DEF.HEADER.LENGTH = "00588"
Too many array elements

[SRSeedBurners]

Based on an old post I found here, I was able to modify this by:

set SMSG^DEF.HEADER.LENGTH[2]=53

print SMSG^DEF.HEADER.LENGTH
$5 = "00588"

Super ugly way to do it, but that's what I found.