Replacing Prefab Instance with variant

Hello,
I'm trying to write an editor script which automates replacing prefabs while preserving modifications made in parent prefab as overrides and references to children of nested prefab.

I use YamlDotNet parser to traverse the prefab, find PrefabInstances and replace proper guids. So far with this method I can replace prefab with another prefab and preserve modifications but if I use prefab variant instead modifications are not applied in the editor.

After short investigation I have found that m_CorrespondingSourceObject fileID mismatch is causing the problem but I can't find a way how to get proper fileID. In case of a regular prefab fileID simply matches document id in referenced prefab asset file but with variant I have no idea where does it come from. I looked through the .prefab and .meta files of base and variant prefab with no luck. I assume it is somehow calculated with some kind of hash function based on prefab name but I'm not sure.

Any help is appreciated!