The trustee values the property as of the date it is sold. The equity that has accrued since you filed goes to the estate. Any equity you have over your exemption can be used to distribute to creditors.
Technically, your assets are valued at the time of filing, however, as a practical matter, if the trustee can show that there is some equity at the time of filing due to an undervaluing, he/she can let you pay the difference between the actual value at time of filing and your exemptions. You should contact your attorney (if you have one) or an AVVO attorney for a free consultation. Good luck
The trustee can sell the house, and you can argue your position before the judge. You need some local case law to know if there is support for it. As suggested, the better route may be to negotiate a lump sum payment to the trustee so the sale can be avoided.
As the other attorneys have pointed out, your schedules are required to reflect the value of the property as of the date of filing. However, if the trustee conducts his own review of the property and determines it was worth more than you scheduled, it can be an issue if you are over the exemption amounts. Additionally, the equity accrues post-filing to the bankruptcy estate which would also enable the Trustee to go after the asset if he/she determines you're again over the exemption amounts.