Unfortunately, at present, there is no 'step-up/step-down' facility to be used in conjunction with Final Salary pension schemes to change from no escalation to escalation as time goes on.
As a 'workaround' you can add the current pension in payment as Other Income, showing it as Taxable, set to stop at the point the pension starts to escalate, ensuring growth is set to zero. Just be aware that this payment will be treated as 'self-assessment' income, with tax being paid annually-in-arrears (as opposed to PAYE, for the Final Salary benefits). Also, Other Income either survives the owner on death 100% or not at all. If the pension income survives the owners death at a different rate e.g. 50%, and you want to model early mortality prior to the point the pension starts to escalate, you would need to manually step this income down at the early mortality event.
To model the escalating pension in the Final Salary screen select Deferred, starting at the age at which the pension starts to escalate, with Escalation in Payment set to the appropriate rate.
As is the case with Money Purchase schemes, the software assumes (by default) that final salary benefits will commence payment at an individual's Retirement event - where this is the case, no further action is needed.
Where this is not the case, go to the Time panel located on the right side of the screen. For defined benefit schemes, a selection on this panel will be used to indicate the point at which benefits are to commence payment.
When in the Final Salary screen, select the Deferred pension you have created from the ledger. Select the Event tab. If you don't already have the appropriate event on the timeline, a new one can be easily added by clicking the New Event button, located in the bottom-right corner of the Time panel, Event tab. Select the event at which benefits are to commence so a green dot appears next to it. Click Update.