I would like to run a version of Bitcoin Core from 2013 along with my normal Bitcoin Knots 28 that I have installed and has the full blockchain downloaded and validated (which took a lot of work to set). So my question is: How do I install an older version of Bitcoin Core and use the existing files, but not have them screwed up?

My idea is to simply install Bitcoin Core 2013 version in other folder, and it should use the /.bitcoin folder to get the block files. But my concern is that instead of using the existing files, it's going to do something to the files or something that forces me to validate or even download the entire chain again which is hell.

I want to do this because I want to convert a 2013 wallet into the new format. And I want to do it with testnet coins first, so I don't screw up with real coin wallets. But I need to download Bitcoin Core 2013 first to create a 2013 .dat wallet file. Then I want to be able to migrate it into the new format, and then create a watch-only wallet for an online node in another laptop.