Hello tricia63. This is an interesting question which doesn't have a simple answer.
To become registered as a disabled person in the UK the condition has to affect you in such a way that you would be considered permanently and substantially disabled. As far as I know there is not a list of conditons to qualify people to be registered as disabled. Many people with stomas are not 'disabled' by the condition even though it may be permanent. So, it is very specific to the individual and usually comes down to a judgement call by a social worker or an OT and they require confirmation of the effects of the condition from a medical practitioner.
You could put forward the argument that your condition necessitates a need for access to disabled toilets and, if it 'disables' you in any other way in your daily life then you should add that to the list of things to bolster your argument.
I became registered as disabled because of my severe faecal incontinence before I had the stoma. It got to the point where I could not walk around because that would make me incontinent. I argued that I needed a bicycle for transport so that the saddle would keep the anal plug in place and they agreed with my logic and registered me as disabled at the same time as writing me a letter confirming that I needed a bicycle for mobility purposes in the same way that other people needed wheelchairs. They also offered to authorise a Blue Badge parking permit so that I could park near to public toilets but I declined that because with the bicycle I could and would ride right into the loos and it did not pose a problem being any distance from them.
I would suggest that you make a comprehensive list of all the facets of stoma life for you that make you feel 'disabled' and then make an appointment with your GP to see if they would support you. Then see someone from social services (either a social worker or an occupational therapist - depending on who your local Social Services Department have designated the task to) to discuss the registration process and assess whether you would be eligible.
Oh! and a useful tip would be - make sure you are putting across the worse-case scenario.
Nothing ventured nothing gained.
Best wishes
Bill