Can I extend the expiry date of my TIER 1 visa for 2 months

[Antar]

if I change my planning and postpone the date of my travel after I got the visa, can I extend or "move" or postpone the expiry date of my visa for 2-3 months? ( to move the two year window for 2-3 months)

is that possible if I have good reasons?

[PaperPusher]

It is not possible. It is possible to request post dated entry clearance only.

[Antar]

It is not possible. It is possible to request post dated entry clearance only.

and how to request that?

[vinny]

Enter the expected travel date when applying. It may be too late to change the visa if it has already been issued. However, there's no harm in asking them.

[Antar]

Enter the expected travel date when applying. It may be too late to change the visa if it has already been issued. However, there's no harm in asking them.

note: I'm eligble to the enter the UK without visa for a visit.
now if I go what do I need to do, do I need to show them the visa?
what they do for me?