Is the 19-A tax update required for year end/T4 processing for Canada?

We are currently on 18-E, and I need to start planning for the 19-A tax update. Because of resourcing, we will have some difficulty immediately patching to 19-A. Does anybody have a "sneak peak" of what is being changed in 19-A as it pertains to Canada? If possible, we would prefer to delay updating to 19-A, perhaps combining it with 19-B. But our payroll will be processing T4s in mid February, so if there are sqr or other changes in the update affecting Canada year end, we'll have to figure out a way to get our system updated before that