Modify structure

Hi

I don't know whether it is possible or not, but I often are in need of modified the structure of a compound to a metabolite, e.g. venlafaxine to N-desmethylvenlafaxine. The metabolite of the parent compound is not present in great extended yet of chemicalize.org.

So what I'm asked is, are there a function to take the structure of a parent compound and modify it to a non-existing compound in chemicaliza.org in the drawing board without having to draw the whole structure from scratch ?

Thanks in advance!