Yes, you can just CAL the ohms without doing any other function, (indeed any of the other functions can also be done singularly to), but be wary that trying to do the short and open tests of the 'ohms CAL' alone will not do it seems.
I just tried that with the replacement meter, ie doing the 'Short and then Open' part only and then exiting the adjustments without doing the complete ohms CAL.
And when the meter restarted with no leads connected the display showed around 5M
on the display
. I noted that behavior with the 'modded' meter but thought I did something wrong and dismissed it as I went on and did the full ohms CAL.
So my recommendation would be do the mods and check as best you can (comparison with other Meters etc) that its still within spec. and don't try the CAL unless you have the required stable known resistors to hand. IIRC as I stated earlier only the ohms and possibly the DC current zero's shifted a bit and adjustment was not really needed.
Remember the NULL function. I have noted too that the ohms zero will drift around a few counts anyway (temp. related!).
Also I did not bother with any matching of the resistors.
Having access to the required calibrator has made it easier for me of course to do the CAL. but I would have been happy leaving it as is. Particularly if cross referencing with other meters gave similar results within their respective specs.
An interesting side note, when I checked the number of CAL cycles the new replacement 1272a that Keysight sent me it had already done 15
....... go figure.