Given the following time breakdown, should a person have their resume target a developer job, a support job, or something else?
60% of the time is spent supporting existing systems. This could include taking calls from end-users, fixing production issues, etc.
40% of the time is spent doing development activities The development work could include enhancements to existing systems, or the building of new medium-sized applications.
I guess it's a but unusual to have a person focused on both support and development, but in this case at the split is fairly even it would be good to have someone who was strong in both areas and didn't want to move into one of the areas specifically.
If I were advertising this role and saw a resume focussed heavily on development then I would consider that this person was trying to move in that direction, even if they had a good support background. Doesn't mean they couldn't do the job, but they might not be happy with the heavy support load.
I'm not sure if you're hiring this position and looking for people or you've found the position and are looking to submit your resume, but my answer is more focused on the hirer I think, hope it's helpful.
Don't have only one resume.
Always target your resume to the job you are applying for. If you are applying for developer jobs, submit a resume focussing on your development skills. Similarly if you are applying for a support job, submit a resume focussing on your support skills. If you are applying for a job as a waiter, focus on your customer interaction skills, etc.
Always include a covering letter that highlights the ways your resume and experience target the selection criteria.
Good luck.
To my mind, it depends entirely on where the person wants to go as this is one of those, "either or both," situations depending on what job the person is trying to get. If this the objective is to be an open one to a recruiter that may want people of either desire, then the key would be to note that the person is comfortable handling either side of what a developer may do in their job.