Yes, you can. It could cause you to be placed in a higher tax bracket. The income you earn from employed work is taxed by the tax bracket 1. The Tax Authorities adds both gross income products together. If your gross income increases because you became a FreeFlexer, this would mean that your income will partially be taxed in a higher tax bracket. Read the article on 'tariffs and tax brackets' by the Tax Authorities for more information.