Currently this is not possible, but I will consider this feture in the future. (it is not so simple just to add this)

Regards

Tony

Can I use setColProp to add a new column? If not, is there another way to do this?

If not yet possible, the function should be rather short right? Is anyone able to write it and add it to the min-versjon of grid-custom.js or something?

I don't know but perhaps if similar to setcolprop then
addCol : function(colname, obj){
  this.p.colModel[this.p.colModel.length+1] = obj;