There's not much reason a change of leadership would touch off much of a change. Ferdinand was an unknown at the time, and wasn't hated yet. The mother country wasn't a shambles.
Sure, you have the underlying Criollo vs peninsulars vs the common folk/native population and the feudal society thing, but it wasn't at the powderkeg point with the Spanish world still seeming relatively stable, so Ferd coming to power isn't much of a spark. he's only 16, though, so I guess it represents an opportunity while there's a power struggle in Spain looking to see if Godoy can hang on/who gets to be regent. Then again, Momma runs the show anyway while Charles hunts, so there probably isn't much of a power shift. Just switch one figurehead king (husband) to another figurehead king (son). The power struggle then gets delayed til Ferdinand comes of age and tries to take over from Mom, but that doesn't really satisfy the OP of speeding up the revolution by much. It does present butterflies for the Nap wars/Spain. the whole kidnap the kings thing on a pretext of settling the 'who is king' dispute goes away, and that is HUGE for the spanish america revolution situation.