Lemurs, Baobabs & the Eighth Continent
No. Working on a tourist visa is illegal. You need either a work visa sponsored by an employer or a business visa through EDBM. NGO and volunteer work also requires the appropriate visa category. Enforcement is inconsistent but penalties can include deportation and entry bans.
Malagasy citizenship can be obtained through marriage to a Malagasy national (after 5 years) or through naturalisation after 10 years of continuous legal residency. Dual citizenship is not recognised by Madagascar — you must renounce your previous nationality. Most long-term expats maintain residency permits rather than pursuing citizenship.