Is it possible to perform a turbo replacement for a 1.9 dTi? Self-assembly possible?

Hello Diesel Enthusiasts,

here the continuation of my problem: Extreme performance loss b. Renault 1.9 dTi, 28.4.02

The problem seems to be solved thanks to the helpfulness of several forum members (including those from fmso+mykangoo.de).
The owner of the car had had it converted to run on plant-based oil.
Here, the fuel pump failed. New Bosch ESP installed.
The conversion has been completely removed.
During the oil change, a significant amount of vegetable oil was found in the engine oil. It seems like something has been forced into the fuel injectors (how does this work?).
Therefore, this oil mixture is likely to have caused damage to the turbocharger.
Also, it's also conceivable that the VTG could be stuck (like the 1.9 dTi).
Definitely, the turbo will kick in after the tips and tricks mentioned in this forum.
not mentioned criteria. Follow: Complete loss of power (only 60 hp remaining)

My question to you: Can Turbochargers be restored after a bearing failure, or can they be cleaned if they are 'stuck'?
If so, how can I do that, or where can I find such companies?

If not, how much would such a turbocharger cost with installation (can it be installed by oneself)?
Can I also buy the turbo at the auto parts store or do I have to go to Renault?

I would like to thank you in advance.
I am particularly impressed by the solidarity in the forum.

Best regards, Klaus