It sounds to me like you’re trying to do style transfer from one sentiment to another. This is an active area of research currently.
One of the most popular papers is linked below but doesn’t use transformers:
  
      
      ACL Anthology
  
  
    

Delete, Retrieve, Generate: a Simple Approach to Sentiment and Style Transfer 3

Juncen Li, Robin Jia, He He, Percy Liang. Proceedings of the 2018 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies, Volume 1 (Long Papers). 2018.


  
  
    
    
  
  


And here is a paper that builds on those methods using transformers:
  
      arxiv.org
  
  
    
2005.12086.pdf 3

338.76 KB

  
  
    
    
  
  


Best of luck