Magic fields in WikiText

Greetings & Salutations,

How hard would it be to have wiki text custom fields handle magic
placeholders like ID, etc?
I looked at share/html/Search/Elements/BuildFormatString, but it does
not seem it can be easily
(ab)used for this…

Although I think this can be a generally useful thing, in my case I
intend to use it like so:

A ticket is created with missing information, and a stub is placed in
a wikitextarea linking to
another RT page (Users/Modify.html?Create=1). I’d like to append the
ID of the offending
ticket to the URI so that I can have some callback or local version of
Modify put the ID of the
new user into the custom field of the original ticket, replacing the
creation link stub.
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