2 offers- attestation process started- what do/can I do

I have received 1 offer which I accepted for a job in Saudi. I accepted the job offer and begun the attestation process via the saudi cultural bureau in UK about 6weeks ago. 

Now I may receive another offer for another post. I think this second post may be better for me in the long term.

Given my attestation process has started (no visas issued yet or anything), can I now decline the first offer and start the job process for the 2nd offer?

I am guessing I will need to get my document re-attested from SACB as the first attestation will be with a letter from my 1st employer offering me the job.

Are there any unwritten rules regarding doing this?

thanks for your help