Changing term on Life assurance

We plan to get a get a variable tracker of 30 years initially with the aim of reducing this down to 25 years within the year. However, will we end up paying a higher life assurance policy due to the initial 30 years, or can we get this reduced as soon as we reduce the term of the loan. I've changed life assuarance policies once and to be honest, they made it so difficult that I'd need to save 1000s before I'd change again. If we end up paying over the odds for the initial year of lower payments, then I think we'd just stretch ourselves and go for 20 or 25 years straight off. Any advice would be much appreciated. Sorry - one more question, does anyone know what rate of commission a broker would get for securing your life assurance policy,
Thanks,
C

Brokers could earn up to 90% of the first year's premium in commission on a life policy, with the possibility of further commission for renewals.