man xfmconcat (Commandes) - concatenate MNI transform files
NAME
xfmconcat - concatenate MNI transform files
SYNOPSIS
xfmconcat input1.xfm [ input2.xfm ... ] result.xfm
DESCRIPTION
xfmconcat concatenates a number of transforms together. The resulting transformation will have the effect of applying transformation input1.xfm then input2.xfm, etc, in that order.