That shouldn’t be done
Re: Diplomatic passport for former Head of State
You’re essentially asking for the perks of office to continue long after the office holder has left the job.
I agree with some kind of a superannuation package for all former Heads of State and continuing (slimmed down) protection by the Samoa police special diplomatic protection squads.
However, a diplomatic passport is for official state business.
All bearers of such passports travel in their official capacities on behalf of the Government of Samoa. Former government officials, even if he is a former Head of State, are no longer in that category.