Thanks for the link.
We can perhaps see that the metabolite dextrorphan (DXO) would lend itself to acetylation but:
1) one would have to isolate the DXO; and/or
2) non-enzymatic preparation of DXO is also non-trivial, requiring dangerous reagents such as BBr₃ and therefore unsuitable for "kitchen chemists"; and
3) acetylation of DXO would also require at least one hard-to-obtain reagent.
4) if interpreting the OP's question more strictly, then adding a carboxy group to DXM is even less trivial and would require other dangerous and hard-to-obtain reagent. Since I suspect that the OP's intention was something other than preparing an antidiabetic agent I shan't be going into further detail here.
Probably the most important thing, chemically speaking, that one should take away from this is the difference between an acetyl [*in this example, an
O acetyl] derivative and a carboxy derivative. Put simply, the former can be represented as ROCOCH₃, the latter as RCOOR'. Notice that the former has oxygen bonded to the main part of the molecule (R) whereas in the latter the bond is to carbon. Broadly put, acetylation at oxygen is somewhat easier than carbonylation of an aromatic group.
I would also suggest to look into tho properties of O-acetyldextrorphan but, as _Trip_ has pointed out, that is not the focus of this site.
PS - "DXM carboxylate" is no one specific compound hence the comment on nonsense chemistry.
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli