Yes, Bogen/Manfrotto heads are easily replaceable. There are many combinations available.

The attachment is simple. There is only one main screw holding the head to the tripod's base plate, a ⅜"×16 on full-size tripods, or a ¼"×20 on smaller ones. To prevent the head from unscrewing from the base plate, there are also three screws through the tripod's base plate which engage ramps in the head's mounting surface. You can see them by raising the tripod's center column and looking at the bottom of the base plate.

To remove the head, just remove the three anti-rotation screws with a screwdriver, then unscrew the head from the center column by hand. You don't need tools for the second step because the anti-rotation screws obviate the need to torque the head and tripod tightly together. The head shouldn't be any harder to twist off than a mayonnaise jar lid.

This system is pretty well universal. You don't have to get a Bogen/Manfrotto head for your Bogen 3221 leg set. Anything with a ⅜"×16 mounting screw can be made to work.1

Can I replace this with something else? Something that has gears...

Manfrotto does have geared heads, such as the model 400:

Personally, I prefer a three-way head:

I find that it offers a nice compromise between precision and speed of adjustment.

I started on a Bogen 3030 3-way head2 about 20 years ago now, and I still like that head. I've tried a few different ball heads, and I'm with you: they're too easily adjustable for the kind of photography I like to do.

I do like the quick-release part.

Manfrotto has several QR plate systems. The one on your current ball head is the old "RC" plate, also known as the Bogen 3157.

It's been replaced by the RC2 plate design, which has the same overall plate size, so the new plates will still work on old RC series heads. The RC2 heads have some material removed relative to the older style, and some of the newer Manfrotto heads have QR mounting areas that require that these cutouts be present, so that the old RC plates won't fit.

The geared head depicted above is yet another plate design, which I have no experience with.

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Footnotes:

1. There are companies making only tripod heads: they just use the standard mounting system, knowing their heads will work on leg sets from several other companies.

2. a.k.a. Manfrotto 141RC