i did this once, but it's been a while, and it actually worked.
same issue, hardcoded code to three part naming conventions.
it's been a while, but i obviously made sure i could convert text-->varbinary-->varchar and then back again first.
since all i had to do was spin off a backup of the ReportServer database, i was not to scared to make potentially devistating changes.
in my case, i selected all the converted content first, and found i had to make multiple updates, due to patterns not being 100% consistent...sometimes things were quotenamed, sometimes they were not. i modified just one report as a proof of concept, and after i confirmed it modified with no issues, i did it against all the reports that matched the pattern/problem.
convert(varbinary(max),cat.Content)) As Verted,*
FROM ReportServer.dbo.Catalog cat
where cat.Content is not null
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