The Admissions code has several paragraphs on when and who to consultations to changes in admissions must be conducted (an increase in PAN is not a change in arrangements though).
From the code, if admission authorities wish to change criteria, they must hold a consultation. In reality, what this often consists of is putting the new criteria on their school/LA website and inviting comment, as well as sending the new criteria to the admissions authorities of local schools. Those local schools might then put a note in their newsletter to parents about it, but they don't have to.
from the code -
1.46 Consultation must last for a minimum of 6 weeks and must take place
between 1 October and 31 January in the determination year.
1.47 Admission authorities must consult with:
a) parents of children between the ages of two and eighteen;
b) other persons in the relevant area who in the opinion of the
admission authority have an interest in the proposed admissions;
c) all other admission authorities within the relevant area (except that
primary schools need not consult secondary schools);
d) whichever of the governing body and the local authority is not the
admission authority;
e) any adjoining neighbouring local authorities where the admission
authority is the local authority; and
f) in the case of schools designated with a religious character, the
body or person representing the religion or religious denomination.
1.48 For the duration of the consultation period, the admission authority must
publish a copy of their full proposed admission arrangements (including the
proposed PAN) on the school’s website or its own website (in the case of a local
authority) together with details of where comments may be sent and the areas
on which comments are not sought. Admission authorities must also send,
upon request, a copy of the proposed admission arrangements to any of the
persons or bodies listed above inviting comment. Failure to consult effectively
may be grounds for subsequent complaints and appeals.