If two nations with a common border consensually decide to shift it this way or that, draw up and sign the paperwork, then no problem.
In Africa the problem is rather that you have now a centralised authority very far from the borders, and the borders are where all kinds of larger or smaller ethnic groups have been divided up one upon a time.
What are you going todo with the Zande for example? The 19th c. Azande empire (under the Avongara princes) controlled and area the size of France. They and the Maasai were the only political entities in central Africa able to make the Arab slavers skirt their territory.
Being that militarily capable of course they got broken up between the Belgians (Kongo), French (Congo Brazzaville, French Congo) and the British (Sudan as an Anglo-Egyptian protectorate).
Neither of these modern states have any interest in erecting a Zande state even if that once would have been what was politcally feasible and reasonable.
The time to do this different would have been the 19th c., but then the Europeans would have had to let king Kabarega of Bunyoro and his 1500 troops with European rifles (Snyders and Jocelyns) fight it out with his neighbours to settle what would be a viable African state.
Or concluded that when the king of Dahomey in the 1890's equipped his army with machineguns, then perhaps he should have been left alone, as he hoped through that move. But France didn't so now the point is moot.
So much has happened since then to make it impossible for Africa to pick up where the Europeans interrupted them.
Attempts to change borders in todays Africa are all civil wars. Katanga tried to break out of Congo in the 1950's and got jumped by the UN in fact. (Gen. Sec. Dag Hammarskjöld really went to war good and proper on that one, and died in it.) And in the 1960's Biafra tried to break out of Nigeria, and got slapped down, hard.