The assessors shall make such assessments and valuations of subjects of taxation each year preceding the triennial assessment in such counties, and shall file the same with the board on or before the first Monday of September of such year. Assessment of occupation after being once fixed shall not be changed during the triennium, except by the board upon the appearance and affidavit of the taxpayer. The assessor shall, in the year immediately preceding the regular triennial assessment, make occupational assessments for all of those in his territory who have become of age since the creation of the last assessment and all of those who have moved into the territory since the creation of the last assessment.

The county and each city, borough, incorporated town, township and school district may, by ordinance or resolution, exempt any person whose total income from all sources is less than five thousand dollars ($5,000) per annum, from its occupation tax or any portion thereof. Each taxing authority may adopt regulations for the processing of claims for exemption.