A Company comes into existence from the date of issue of Certificate of Incorporation issued by Registrar of Companies. Before that, it a proposed company only.
Once the COI is issued, the change in any parameter of MOA or AOA would require approval of BOD/ Ordinary Resolution by shareholders/ Special resolution by shareholders, depending upon case to case.
Before incorporation, there are no shareholders but only subscribers to the company. They are to be minimum 2 for a private limited company and 7 for a public limited company as per Company's Act,1956.
Any modification in the structure of the company, before the COI is issued, can be done under the signatures of initial subscribers like leaving of an existing subscriber, joining of a new subscriber etc., by informing the ROC and revising the draft MOA.
As regards promoter, there is no such thing in the Company's Act,1956. All the initial subscribers are said to be promoters though they may be holding different number of shares. The person having maximum number of shares has the maximum voting rights, so he/she controls the company after incorporation.
If the initial subscriber having maximum number of shares wants to leave before incorporation of the company, his shares can be subscribed by the existing subscriber(s) or a new subscriber and accordingly the MOA submitted to the ROC of the proposed company will have to be revised.
Even after incorporation, the Directors/ initial Subscribers can leave the compnay at their free wil by selling their shares. Only the removal and appointment of new Directors would require shareholder's approval.