Following from Peter's answer, yes - both the base/ neutral expression CC avatar model and all animation morphs can be modified/ reshaped as long as the mesh itself (vertex number and index) remains unchanged.
To modify the animation morphs - you'll need 3DXchange pipeline: load your avatar and scroll down to the Face Setup panel on the right hand side of the UI. Here, you can select an animation morph and export it for external modification - then use the 'replace' function to slot the modfied animation morph back in.
Also in the same panel, you can if you wish select the base avatar mesh - and you'll see buttons activate in the small 'Replace Mesh' panel below Face Setup which allow you to export and replace the base (neutral expression) avatar too: this provides an alternative path to modify an avatar - purely in external tools, outside Character Creator.
The Face Setup panel also allows you to add custom morphs - so yes, you can go over 60. Custom morphs can be used alongside (or as alternatives to) existing morphs by applying them to particular expressions in the Expression Editor. They can also be used independently in Face Puppet by setting them up as custom morphs - again in the Expression Editor.
The most important thing to bear in mind is - as I said before - not to alter the CC mesh structure, only its shape.
I hope that helps -