SQL Server 2008 R2 Edition Upgrade Process I have several SQL Server 2008 R2 Standard Edition instances that we need to upgrade to SQL Server 2008 R2 Enterprise Edition.

If I have valid SQL Server 2017 Enterprise Edition (with SA) PIDs, do I need to have SQL Server 2008 R2 Enterprise Edition media to complete the upgrade?

Please don't recommend that I upgrade to SQL Server 2017 - it is not an option at this time. It has taken years of pleading with management to upgrade to a newer version, and 2+ staff years for regression testing. It has taken an order of magnitude increase in Transaction Rate/Database size to even get the edition upgrade approved.

The question is how to perform the edition upgrade, not what the licensing implications are.

Our thought was that running SQL Server Installation Center and choosing Maintenance -> Edition Upgrade might work since the basic bits are probably the same between editions.  My guess is that the only differences are some run-time switches, configuration values, etc. so the Enterprise Edition media might not be required?
You will need to use SQL Server 2008 R2 Enterprise Edition media to perform the in-place edition upgrade.  I am unaware of any option available that allows you to perform an edition upgrade without a version upgrade when using media from a different SQL Server version.

Will your licensing agreement cover this?  That wholly depends on your licensing (though I highly suspect it won't), but that question is best sent to your license partner/reseller.

If you have a MSDN license, you may still be able to pull down the binaries for SQL Server 2008 R2, so that would be one way to get the required media.