I have managed to add an extra field to the member table through a dataobjectdecorator and I have also managed to get it into the member form that you get when you press edit on the complexTableField on the member table.
However I can't find where the fields for the complexTableField are made/added. I would really like to get my dropdown list on the complexTableField since right now you first have to add a member and then edit which is very clumsy/unintuitive.
I must also say that the documentation around modifying the member table is very lacking. A simple tutorial for decorating the member, adding a field to the member form and getting it on the complexTableField would go a long way to helping alot of people when it comes to member modification I think.
I actually figured this out but forgot to report back.
There is a function called addMembershipFields on the MemberTableField class. You can calll it like I do below.
You are however severely limited in what kind of fields you can add since addMembershipFields only takes the fieldname and the title, not what kind of field you want. Because of this you'll always get text fields.