TL;DR Yes, you can edit clipping masks after you create them using any traditional vector editing tools. You would click anchors and move them or adjust Bezier handles. But no you can't just "paint and erase" things in Illustrator like you do in Photoshop. That's not how the tools work in Illustrator.
It is first important to understand that The Brush Tools and the Eraser Tool in Illustrator completely unlike brushes/eraser in Photoshop or other raster-based applications.
Raster-based applications alter pixels within an image. Brushes paint on more pixels or change existing pixels, and the eraser removes pixels.
In Illustrator, brushes draw spines or paths which an appearance is then applied to. No actual pixels are created. The Eraser in Illustrator us used to cut shapes or paths and remove sections of a path/shape, no actual pixels are removed. (This can be confusing since all monitors use pixels to display anything, but Illustrator does not contract anything based upon pixels).
Basically... Think of Photoshop et al as being a traditional painting, just like you would paint on a real canvas - only pixel-based. However, Illustrator is far more akin to a construction paper "decoupage" - it is object-oriented and not pixel-based.
You can't just paint and erase in Illustrator like you can in Photoshop. That is not how the tools in Illustrator work.
Regarding masks: They are very different in Illustrator when compared to Photoshop or Fireworks.
Illustrator has 2 basic mask types -- a Clipping Mask and an Opacity Mask.
A Clipping Mask is constructed of a path which is then used to "clip" or "hide" anything outside that path. It's just a vector path and can be edited using any traditional vector path editing techniques. But you can't "paint and erase" the path like you would in a pixel based application. In addition, clipping masks are 1-bit masks. That means you either hide or show content. There's no such thing as a 50% opaque clipping mask. An object is either masked entirely or it's shown.
Opacity Mask are a bit different. And Opacity masks can be similar to raster application masks in that 100% black hides and 100% white shows, grey levels show various levels of opacity in the mask. Opacity masks can be constructed using vector objects or embedded raster images. But you still can't just paint in pixels or erase pixels.
