Inserting unicodeText into a unicode string?

[Richmond]

[Working on my G4 MacMini at present]

So here I am with a long unicodeText string in a field and I want to put 
some more unicodeText inside it
(where I set my cursor) . . .

Adding text at the end is easy:

Set the unicodeText of fld "XYZ" to the unicodeText of fld "XYZ" & 
numToChar(50000)

Adding text at the start is easy:

Set the unicodeText of fld "XYZ" to numToChar(50000) & the unicodeText 
of fld "XYZ"

HOWEVER: I want to put my cursor somewhere in the unicodeText in fld 
"XYZ" and
add my numToChar(50000) there . . . .

Love, Richmond.