Neither the Declaration of Independence or the United States Constitution mention slavery by name, and only spoke of it obliquely. The best that the FF could manage was to set a date for banning the continued importation of slaves to the country. The southern states held that much clout that our nation wasn’t to be unless we accepted the Peculiar Institution.
When the rebels put together their confederate constitution they borrowed heavily from the real one - very heavily. But one of the most notable departures was the enshrinement of the institution of slavery. Constitutionally mandated for all time.
This doesn’t strike me as anyone with an inclination to change anything. Not when it was important enough for them to wage war with their brethren just to maintain it.