Hi Mack,
I'm in touch with Chris McLean at CWGC. He's works manager, rather than commemorations, but explained the process. The family need to agree the erection of a new headstone (HS) on a private plot, where there is no private HS, or the inscription can't be read. They use the standard HS on most burials, but use the Gallipoli style lower HS when the two uprights commemorations would look bad, or sometimes in Ireland where a more subtle approach is best.
If CWGC take over an existing HS, they maintain it and keep it safe. Chris has dealt with one of the Regiment's graves at Aldershot, where a stone cross looked dangerous. He also said they would remove bushes and vegetation, so that the inscription can be clearly seen. I don't know if they can renovate a private HS though.
We can't press for a HS on existing plots. If there is no known plot, or no consent, inscriptions will be added to existing screen walls, or special memorials. If there is none, or no space a new HS is erected with the script "Buried Elsewhere in this Cemetery". These can have mutiple names, which I think will happen for the common grave burials at Weaste. Sometimes combining across multiple HS.
We're missing information on many burials, so any help taking photos of plots would be great. PaulC has provided a few at Chadderton.
A CWGC HS on the specific plot would seem to be the most appropriate commemoration. There will be numerous instances where family consent will be needed, so starting to find them ahead of adjudication will help. CWGC do release names of men where they're seeking contacts, but I don't know how succesful these are.
Family members I've contacted are very receptive, though I've been keen to remind them we have an application, not acceptance of a commemoration.
Entries on 1914-18 Memorial are great, screen walls and Special Memorials are better, but specific HS on the man's grave would be best.
I wish I lived nearer to Manchester.
Tim