Severe Disability Premium and UC

Hi,
a little advice needed.
I have been on IR ESA for some years and did have the Severe Disability Premium as I am on qualifying PIP criteria etc.
I informed DWP of my eldest child turning 18 last summer and that I was no longer entitled as effectively an adult was now living with me. They removed the SDP entitlement. However, my eldest has now moved out and I informed DWP today and the call centre lady has passed on my request/claim to have the Severe Disability premium re instated from the date she left. Council etc were informed and it seems the DWP will now process my request ( I still qualify both financially and by virtue of the PIP standard rate care.
Question is this: It only dawned on me later that this might be classed as a chance of circs and trigger my having to claim Universal credit earlier than I had expected.
I doubt it as my area hasn't gone fully live yet and will be amongst the last to do so and it isn't really a change as such, merely a request to have the SDP added to my existing ESA claim. The lady I spoke to didn't mention having to make a fresh claim or anything.
Can't find anything conclusive online so any advice will be appreciated from the mods.
Thanks.

Thanks Gordon I have found some relevant stuff since posting this thread If I understand you correctly it would only trigger C O Circs and UC transfer if I had to claim what is called a Legacy Benefit. i.e. new claim for ESA JSA I/S CTC etc As it stands this is merely an adjustment to my existing ESA Ben. so shouldn't trigger UC. Correct?