回複：這個offer可以／應該negotiation嗎？

I think it should be OK to negotiation. It is not finalized.

I had an experience before. I got my official offer, but did not like the salary. I did negotiate several times, and got three official offer letters. We finally reach to an acceptable salary with the promise to get me a big raise a year later.

In fact, he did not keep his promise after one year, then I changed my job to get another higher pay position.

It is negotiable, but you should be flexible according to your situation and job market. I might not be able do the same thing today at this bad time.