I have tried this in modo 14.1 and 14.01
I can create a material preset, and assign a material with an Octane override to it.
It works fine, I can change the linked preset while the file is open.
As soon as I re-open the file, it tells me there is an error, it cannot create the override, and the scene crashes automatically.
I get the following message before the crash (see attached), as soon as I try to re-open the file.
I have contacted Foundry as well about this