Rosegarden considers a composition to be accompanied by a single stream of “tempo changes” and “time signature changes”, which you can edit to adjust the tempo and the number and structure of beats in each bar.

A tempo change can be to a constant fixed tempo, or it can be “ramped” — changing smoothly to a different target tempo at a given future time. Each tempo change takes effect until the following one is reached, so any two consecutive tempo changes together describe a region that will be played at a constant or smoothly ramping tempo.

Tempo and time signature are related, because Rosegarden displays tempo in beats per minute, and the duration of a beat depends on the time signature. Rosegarden only permits a single time signature to be in effect in any given bar; you can't have different time signatures in different tracks. Each new time signature causes a new bar to start, so you can place two time signatures closer together than the natural bar duration in order to obtain a partial bar.