While looking the XML file of my solution I saw this
Does this ID have any practical use or is only for internal use?
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I assume that is a local .rdlc file.
IMHO it has not practical use, in fact you can copy & paste as a new report using the same ReportID and it works.
If you have a look at: RDL XML Schema for Version 2016/01 you won't find any reference to the
<ReportID> tag, or if you get the RDL definition of any report stored in SSRS database, (Where does a published RDL file sit?), you won't be able to find this tag into the file definition.