As of Renoise v2.7.2 only key combinations composed of a non-modifier key and one or more modifier keys pressed at the same time (e.g.: key presses with shift, meta, control, windows combinations) are possible.
It would be nice for future Renoise versions to allow for mapping key sequences, aka a sequence of key pressings and releases. Any element in such a key sequence can be a chord, aka a key sequence in which the keys are pressed at the same time.