Not really, but the effects may not be all that you desire. In particular, attributes are not inherited by "children" of a dataset -- e.g., if you use 3dcalc on a dataset with a custom attribute, the output of 3dcalc won't have that attribute.
AFNI programs read the attributes first and store them in a list. Then the attributes AFNI knows about are scanned for information about the dataset (dimensions, etc.). If the required minimum attributes are found, then a dataset struct is created -- otherwise, the .HEAD file is rejected as unworthy. The order the attributes appear in is unimportant for this process.
See
README.attributes for more info. You can attach arbitrary attributes to the header, as long as they are well-formed syntactically.
If you have some information you want inherited, you could attach it to a dataset in the form of a Note (e.g., 3dNotes). Notes are (usually) inherited by children, since most 3d* programs copy the Notes of the input file to the output file. If inheritance doesn't matter, then attribute away!
bob cox
