Residency status when changing from one nationality to another

Malaysia does not recognise duel citizenship so you should stick to using one nationality for your new job application to avoid difficulties.

Thanks Gravitas. Also, when I get online to do my efiling which for should I fill out? I'm a teacher working for an international school.

To be tax resident you would need to be in Malaysia for 182 days in a calendar year (Jan-Dec). It's time to file for 2017 so nothing to worry about right now.  Your new employer should be able to arrange things for you once the EP is finalised as they deduct tax on a monthly basis and pay it to LHDN under the tax number that has been issued to you. Nationality per se has no effect on Malaysian income tax matters. The issue is recognising a change in nationality due to the rules about dual nationality. Of course you are the same person on either passport, but as a legal entity you are a different person. The only issue therefore (depending also of which nationalities are relevant) immigration may insist you leave the country and be recruited from outside in your capacity as a different legal entity. It's a very niche question.

Thank you for your advice Gravitas. I will be leaving for a brief holiday and returning on the new visa. Question, as a teacher working at an international school (I don't own a business on the side or anything else that generates other tax), what form should I fill out on the efiling website? There are quite a few forms.

Thanks in advance