If you want to compute the replacements based on the item replaced, s///e is very convenient.

s/(?<!0x)([1-9]\d*)/sprintf "0x%X", $1/eg
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I haven't tested this thoroughly, but this should convert any decimal constant in your source into a C/Perl-style hexadecimal constant. It doesn't handle underscores or floating-point well, but it should skip any already-hexadecimal or already-octal numbers.