Question about Chapter 13

[PatsFan]

Hi everyone, first post here. I've been reading the forums for a couple of months now, they've gone a long way towards helping me stay sane!! I'm looking at filing sometime next month. I've used the means test calculator and I'm definitely looking at a 13. All debt is unsecured. I am planning on keeping my home. My mortgage is through Countrywide, so I'm sure they will not reaffirm. It's an ARM and is due to reset in December. Holding off on filing until then is not an option. My question is, when it resets, will I be able to lower my Chapter 13 payment accordingly to reflect the higher mortgage payment? I do not think it will be high enough to leave me with a negative disposable income on the means test, but if it did, would changing the bankruptcy to a 7 be an option? And will the fact that the mortgage would be a ride through rather than reaffirmed have any bearing on this? Thank you all in advance for your help, I'm hoping that the answers to these questions will allow me to begin sleeping again at night!!!