You can always start a new pension plan with a longer duration, but no you cannot change the terms and conditions of the pension plan options you chose at the start – and nor can anyone else. When you have completed your pension plan duration, you can still keep it invested in the same way without having to withdraw it – this is technically not the same as extending the duration of your pension plan, because it will not be in an account type which accepts small regular monthly payments, but will function in a very similar way if you simply want to stop paying into it and keep the money you have accumulated invested and growing until you need it.