@Armando, it should be quite easy to fine-tune with the language modeling scripts.
Let me know if it worked for particularly this model:
  
      huggingface.co
  
  
    

dccuchile/bert-base-spanish-wwm-cased at main 2



  
  
    
    
  
  


I am not sure about it, I tried different models but not all worked for fine-tuning with domain-specific vocab.