https://www.faa.gov/documentLibrary/...0-23_FINAL.pdf
4.2.1…
b. When route or altitude in a previously issued clearance is amended, restate all applicable altitude
restrictions.
EXAMPLE−
1. (A departing aircraft is cleared to cross Ollis intersection at or above 3,000; Gordonsville VOR at or above 12,000; maintain FL 200. Shortly after departure the altitude to be maintained is changed to FL 240. Because altitude restrictions remain in effect, the controller issues an amended clearance as follows):
“Amend altitude. Cross Ollis intersection at or above Three Thousand; cross Gordonsville V−O−R at or above One Two Thousand; maintain Flight Level Two Four Zero.”
(Shortly after departure, altitude restrictions are no longer applicable, the controller issues an amended clearance as
follows):
“Climb and maintain Flight Level Two Four Zero.”
2. (An aircraft is cleared to climb via a SID with published altitude restrictions. Shortly after departure the top altitude is changed to FL 230 and compliance with the altitude restrictions is still required, the controller issues an amended clearance
as follows):
“Climb via SID except maintain Flight Level Two Three Zero.”
NOTE−
1. Restating previously issued altitude to “maintain” is an amended clearance. If altitude to “maintain” is changed or restated, whether prior to departure or while airborne and previously issued altitude restrictions are omitted, altitude restrictions are canceled, including SID/STAR altitude restrictions if any.
i’m sure EASA or the UK ATC ‘bibles’ have similar ‘verses.’
from CAP 493
Amendments to Clearances
When an amendment is made to a clearance the new clearance shall be read in full to the pilot and shall automatically cancel any previous clearance. Controllers must be aware,
therefore, that if the original clearance included a restriction, e.g. “cross ABC FL150 or
below” then the issue of a revised clearance automatically cancels the earlier restriction,
unless it is reiterated with the revised clearance.
Similar care must be exercised when a controller issues a clearance, which amends the
vertical profile of an aircraft on a SID. For example, “climb now FL120” automatically
cancels the vertical profile of the SID. If the profile contains a restriction that provides
vertical separation from conflicting traffic on another SID, the restriction must be
reiterated,
e.g. “climb now FL120 cross XYZ 5000 feet or above”, unless separation is ensured by
other means.
Similarly, when controllers issue instructions which amend the SID route, they are to
confirm the level profile to be followed, e.g. “fly heading 095, climb now FL80” or “route
direct EFG, stop climb at altitude 5000 feet”.
it might not be the most exciting or glamorous pilot activity, but I would suggest you read those big volumes from FAA, CAA, EASA (whatever it is called now) and those of any country you will be based in.