Trustee’s motion to modify confirmed plan to increase payments to unsecured creditors based on tax return showing increased income is rejected: disposable income calculation is not “reset” at modification under § 1329, and only ground stated by trustee for increase in payments is change in disposable income. “[B]ecause § 1325(b) is not one of the provisions identified in § 1329(b)(1) as applying to plan modifications, the issue arises whether the Trustee can require a resetting of the Debtors’ disposable income by filing a Motion to Amend. . . . [S]ince the enactment of BAPCPA, the calculation of disposable income yields a number as of confirmation that is not subject to change upon review at a later date when a modification is requested. . . . The Trustee concedes this point and . . . suggests that some nebulous formula of comparing income and expenses . . . should be used for calculating disposable income for plan modifications. But, there is no authority for that argument. . . . [Section] 1325(b) does not apply to plan modifications. To the extent the Trustee seeks to reset the Debtors’ disposable income under § 1325(b) by his Motion to Amend, the Motion must be denied. . . . Only one of the provisions of Chapter 13 which applies to plan modifications addresses the amounts which must be paid to unsecured creditors. . . . § 1325(a)(4) . . . . [A] hypothetical liquidation analysis must be performed in Chapter 13 cases . . . to obtain initial plan confirmation or approval of a plan modification. . . . [C]hanges in circumstances are relevant to the statutorily-created tests of good faith, best efforts or liquidation analysis, and feasibility, which all apply to plan modifications. . . . [C]hanges in circumstances related to income and expenses may be considered when reviewing proposed plan modifications. . . . The Trustee’s Motion to Amend is not premised on any of the Code provisions . . . . There is no authority for setting—or resetting—what Debtors must pay unsecured creditors other than the specific Code sections discussed above. . . . [T]he Trustee . . . has provided no proof that the Debtors here have the ability to pay any more than they already are paying.”