Hi Dana, thanks for the questions. When making my translation, I made the note:
Adopting the MS main reading of sabbasankharesu anicchasanna. This is the difficult reading, being not found anywhere else. The reading anicca is problematic since it is already found earlier, and since the contemplation is described in essentially emotional terms, non-desire seems more fitting.
The silence of the commentary is noteworthy but hardly decisive, since it only comments on a few of the words in this text.
There is a Tibetan parallel, but it seems that it was a 14th century translation from Pali, so while it might help clarify the accepted Pali reading at that time, it would not provide an independent Sanskrit attestation.
Reviewing the translation, I find neither the points made by Ven Bodhi, nor the points I myself made, to be decisive.
What is decisive, and I should have noticed this earlier, is that this phrase occurs regularly with an exact pair throughout the Anguttara: AN 5.12, AN 4.169, AN 5.70, etc., all have the phrases:
sabbaloke anabhiratasaññī, sabbasaṅkhāresu aniccānupassī
This is identical to the Girimananda Sutta, and they always read anicca, not anicchā. So anicca must be the accepted reading, and I will change it accordingly.
Well, if you’d like to examine all the editions of all the Pali suttas and record all the differences, be my guest. 
We are not Pali editors. We simply present the Mahasangiti edition as we obtained it. There are thousands of variant readings recorded, but for some reason this is not among them.