The apportionment, when finally adjusted, shall continue as the basis of all levies of special assessments to pay all expenditures for organization, construction, improvement, enlargement, extension, damages, costs, maintenance, bonds and interest thereon, and all other expenses; Provided, if (1) there is such a change of plans or enlargement or extension of the work of the district, (2) some of the tracts of land within the district are increased in value since the time of the original apportionment of benefits by the addition of improvements or otherwise, such as in either case to make a different apportionment necessary or desirable, then the board of directors as to the future expenditures shall make a new apportionment of benefits, in which event all the procedure prescribed in sections 31-411 to 31-412 for the original apportionment shall apply, or (3) the board of directors elects to use the tax levy method of financing, all expenditures for organization, construction, improvement, enlargement, extension, damages, costs, maintenance, bonds and interest thereon, and all other expenses shall be paid out of such levies.