Altering custom properties

[Jeff Massung]

Is there a simple way of just changing a chunk in a custom property without
fetching, changing, and resetting it? For example, let's say I have a custom
property "cTest" that has "1,2,3,4,5,6" in it, and I'd like to make item 3
of cTest "***" instead.

I can't do either of the following:

set item 3 of the cTest of btn "foo" to "***"
put "***" into item 3 of the cTest of btn "foo"

I know I can do:

get the cTest of btn "foo"
put "***" into item 3 of it
set the cTest of btn "foo" to it

But I'm just hoping there's a nicer shortcut for me to use instead. ;-)

Jeff M.