I think you are saying you use the same home office for both a W-2 job and your self employment. Yes, you may deduct a portion of the home office. W-2 employees are not allowed to deduct home office expenses. So, for example, during the year you worked 500 hours, in the home office, on your W-2 job and 1500 hours on your self employed work, you may deduct 75% (1500 / 2000) of the home office cost on Schedule C.
I'm of the opinion that "regularly and exclusively" means for paid work and is not limited to your self employment. It does not matter if the work is similar, on the two jobs.
