ETASSUM57100 | Enterprise Management Incentives (EMI): Taxation of EMI options: Disqualifying events – varying the terms of the option
From HM Revenue & Customs · Employee Tax Advantaged Share Scheme User Manual
Section 536 of the Income Tax (Earnings and Pensions) Act 2003 (ITEPA)
Any variation to the terms of the option will be treated as a disqualifying event if it:
increases the market value of the shares that are subject to the option, or
results in the requirements of Schedule 5 no longer being met.