Prior to January 1, 2007, the OMB had a broad power to modify official plan amendments that were before it. Section 17(50) of the Planning Act reads as follows:
On an appeal or a transfer, the Municipal Board may approve all or part of the plan as all or part of an official plan, make modifications to all or part of the plan and approve all or part of the plan as modified as an official plan or refuse to approve all or part of the plan.
The constraints on this power were enunciated by the Courts in Cloverdale Shopping Centre Ltd. et al. v. Township of Etobicoke et al,  2 O.R. 439 at 454 (C.A.) as permitting a broad range of modifications as long as the modification did not change the essential nature or character of the official plan amendment being modified.
This broad power was limited by section 17(50.1) of the Planning Act
, which came into effect on January 1, 2007. It reads as follows:
For greater certainty, subsection (50) does not give the Municipal Board power to approve or modify any part of the plan that,
(a) is in effect; and
(b) was not dealt with in the decision of council to which the notice of appeal relates.
The extent to which the new section limited the former broad power of modification was re-iterated by the OMB in Sunnidale Estates Ltd v. Hobo Entrepreneurs Incorporated  wherein the Board, in dismissing an appeal by Hobo on the basis that the relief sought in the appeal required it to modify policies of the official plan which had not be affected by the official plan amendment, followed the earlier Angus Glen North West Inc. v. York (Regional Municipality) . The Angus Glen decision found that:
This (ed-section 17(50.1)) is not just a friendly reminder. It is a potent injunction against the Ontario Municipal Board to open up (“approve or modify”) an Official Plan or part which are in legal effect and outside the purview of the decision of council to which the appeal notice relates.
Unlike the Angus Glen case, the Board’s decision in the Hobo case was made the subject of a motion for leave to appeal to the Divisional Court. In dismissing the motion, Hobo Entrepreneurs Incorporated v. Sunnidale Estates Ltd, 2013 ONSC 715 (CanLII)
, the Court found favour with the Board’s interpretation of section 17(50.1) as follows:
In my view, the Board was correct in holding that s. 17(50.1) was intended to limit the right of appeal to persons who had made submissions about a part of the OP that was changed by the decision of Council. There is a sound policy basis for such a restriction of appeal rights. Absent such a restriction, anyone who has made a submission to Council as part of the five year review process could appeal to the Board, even where their submissions did not relate to any of the changes implemented by Council. Moreover, as long as they repeated their submissions at the next five year review, the same party could again demand an appeal to the Board every five years on the same issue despite any relevant change to the OP. Section 17(50.1) is intended to eliminate such appeals, and their attendant expense in terms of time and money, and restrict appeals to actual changes in the OP. (page 6, para 19)(ed. underlining added)