From MATS Part 1 Section 1 Chapter 4 Page 4 Para 6.1
"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 FL 150 or below', then the issue of a revised clearance automatically cancels the earlier restriction, unless it is reiterated with the revised clearance."