Create coordinate from dimension?

Hi! I've been trying to convert an existing dimension in my ROMS model output file (e.g. eta_rho) into a coordinate when generating the MultiZarr output. This would allow me to add an attribute to the dimension/coordinate such that it would be properly identified by cf_xarray. I've been messing around with preprocesing and postprocessing to do this and haven't figured it out (yet) but I also keep feeling like it's probably possible using coo_map. I've tried with the coo_map approach a few ways and haven't had any luck that way either. It looks something like

mzz = MultiZarrToZarr(
    json_list,
    concat_dims=["ocean_time"],
    identical_dims= ['lat_rho', 'lon_rho', "lon_psi", "lat_psi",
                    "lat_u", "lon_u", "lat_v", "lon_v", 
                    "Akk_bak","Akp_bak","Akt_bak","Akv_bak","Cs_r","Cs_w",
                    "FSobc_in","FSobc_out","Falpha","Fbeta","Fgamma","Lm2CLM",
                    "Lm3CLM", "LnudgeM2CLM", "LnudgeM3CLM", "LnudgeTCLM",
                    "LsshCLM", "LtracerCLM", "LtracerSrc", "LuvSrc",
                    "LwSrc", "M2nudg", "M2obc_in", "M2obc_out", "M3nudg",
                    "M3obc_in", "M3obc_out", "Tcline", "Tnudg","Tobc_in", "Tobc_out",
                    "Vstretching", "Vtransform", "Znudg", "Zob", "Zos", "angle",
                    "dstart", "dt", "dtfast", "el", "f", "gamma2", "grid", "h",
                    "hc", "mask_psi", "mask_rho", "mask_u", "mask_v", "nHIS", "nRST",
                    "nSTA", "ndefHIS",  "ndtfast", "ntimes", "pm", "pn", "rdrg", 
                    "rdrg2", "rho0", "spherical", "theta_b", "theta_s", "xl",
                    ],
    coo_map = {"ocean_time": "cf:ocean_time",
            #    "eta_rho": list(np.arange(1044))  # tried this
            #    'eta_rho': "data:eta_rho",  # tried this too
               },
    # preprocess=preprocess,
    # postprocess=postprocess,
)

is there an easy way to do this or should I pursue my pre/post processing approach? Thanks.

Start with MultiZarrToZarr and its coo_map handling, using the ROMS eta_rho example in the issue as the case to investigate. Compare the attempted coo_map forms with the preprocessing and postprocessing alternatives; done means determining whether an existing dimension can become a coordinate with the needed cf_xarray attribute, and documenting or implementing the supported path.