Job 40 Expert switching to Technical Job will have to start at Lv. 1 Technical if it's your first time switching to Technical Job.
If you already LEVELLED up your Technical Job, for example if you're Lv. 40 Technical switching back to Expert, you will lose 8 job points because the level loss is level/5 (unless you have memory hourglasses). The penalty applies once you switch back to that job, not when you change jobs.
When switching to your Technical Job, you get to keep four skills from your Expert job repertoire. When you switch back to your Expert Job from your Technical Job, you will be at Lv. 32 Expert Job (40/5 = 8) and you will have to reassign your skill points again.
Any skill points obtained from SP Quests to your Expert/Technical job will not be erased.
Only 3 SP Quests for Expert/Technical are currently available.
You will not have access to your Lv. 40 Expert skill anymore when you switch back because, quite obviously, you're down to being a Lv. 32 Expert.