To be sure, there are several precedents where unitary countries have become federal republics. In my limited research, I learned that the conversion basically involves the formation of one or more local government units of the country into separate and independent organizations enjoying quasi sovereignty with respect to the administration of their purely local concerns while the nation itself continues to possess sovereignty both internal and external under a central government that administers the national affairs. Under the set up, the administration of the national affairs is directed, and its effects felt, not by the separate organization or "state" deliberating as units, but by the people of all the states in their collective capacity as citizens of the nation. The sharing of powers and responsibilities between the central and local governments is fixed by the charter itself. Some States like France reserve a great deal of power to the central government. While others like England allows local authorities a good deal of self-government. But in any case the powers reserved by the central government always include such matters as taxation, foreign and interstate commerce, defense and foreign affairs. So it is not entirely accurate to say that under a federal system, a component federal state will be able to exclusively enjoy its revenues to the detriment of the entire country or the poorer federal states. The framers of the Constitution can and should see to it that the sharing of power will be for the best interest of the entire nation. Indeed the effectiveness of federalism depends to a large extent on how far the localities have a separate tax base. Hence, one of the powers usually reserved by the central government is taxation in order precisely to comply with its internal duties and meet its external commitments. If the local unit or state cannot raise enough in taxation to meet its needs, the central government may offer its financial assistance in return for certain standards being attained or certain programs being undertaken (Politics and Government, Library of Modern Knowledge Vol. 2, p. 673).
Federal member-states may only have the exclusive right to its revenues and refuse to share them with the central government if each of them is fully sovereign and independent, with full dignity, organization and sovereignty, though yielding to the central authority the controlling power for a limited purpose such as external diplomatic relations. This usually happens when the component states are originally independent and separate sovereignties but decide to form a permanent league or alliance under a central authority which acts upon the component units and not upon their individual citizens. This is not a federal system of government. Strictly speaking it is a confederation of sovereign states. It is entirely different from the federal system being proposed for our country. The fear of the anti-federalism on the adverse financial repercussions to our country will therefore never happen even if we adopt the federal system.
There are several reasons causing the development or blossoming of federations out of unitary states. Most unitary countries have become federal republics because of geography like the difficult terrains between the regions or the differences in culture and religion of the population within their borders. But aside from these factors, unitary states convert into federations because of certain advantages. First and foremost, it lightens the load on the central government. The gargantuan national civil service has become too unwieldy for proper and efficient management. Besides, by devolving power to local units, the risk of arbitrary or dictatorial government is reduced. The repeat of martial law is rendered more difficult if not totally prevented. But most important of all, federalism brings a good deal of government activity nearer the public. The grassroots will be more involved in public service and the community spirit will be boosted and strengthened. These are the factors which the framers of the Constitution and the people should know in deciding whether to shift from unitary to federal form of government.