Section 21 - Flexibility for Landlord once issued

Possession - Section 8 and Section 21

Hi,
In light of the Section 21 being banned in the next few months, I plan to issue Section 21's to a Number of Tenants in different properties to enable me to dispose of the properties during this year - which is a fairly likley event.

I understand the requirements to issue a ligitimate Section 21, I have done a few successfully over the years,  but I need to know my options once a notice is issued. Does anyone know the answers to these Qs?

1] Can I extend the move-out date of the Section 21 by agreement with the Tenants. As this changed date would no longer be a Section 21 eviction, would the agreement on the new date stand up in court if the Tenant tried to back out of the agreement? 

2] If I decide not to go ahead with the Section 21 and, after informing the tenant(s),  simply allow it to lapse, I assume that the Statutory Rolling Tenancy will simply continue. Is this correct? Or would I need to formally issue a notice that says I am not going through with the Section 21?

3] I know that no reason is required support a Section 21 but is there any legal risk in my telling Tenants - verbally or in writing - that this is a contingency and I am simply giving myself options to react to interest rate changes and changes in the law against private landlords. Or would I be better advised to tell them nothing?  

Thanks,
 Kieran Sheedy