The modification of ferroelectric vortex domain patterns in hexagonal manganites (here exemplified by YMnO3 and HoMnO3) owing to chemical treatment, thermal annealing, and local electric-field poling is investigated by piezoresponse force microscopy. Chemical treatment transfers the domain pattern into a topographical pattern by domain selective etching. Thermal annealing alters the domain pattern without any sign of temperature memory effects. Local electric fields affect the domain structure with possible signs of electric memory effects. These observations are important for future investigations of the microscopic mechanisms and macroscopic parameters defining the formation of ferroelectric domains in this unusual multiferroic.