Yes. On adding a custom option to a step, from within the step, you will be prompted to select whether you also wish to add it to your Advice Options & Reasons Library. If you check this box, you will then be prompted to confirm whether you wish to share it with your account's other users, and if the step has categories - which category you wish to assign it to.

If none of the categories quite do the job, you can always select 'Other'. Alternatively, leave the category blank and the option will show under the sub heading 'Uncategorsied' at the bottom of the step.

Once created, you cannot change the category the option is assigned to from within the step, but you can do this from within the Advice Options & Reasons Library.