Do you mean he is applying Non-O with a different foundation in April? If he/she is changing the foundation he/she is working for, he/she do have to leave the Kingdom in order to apply.
If this person is staying with the same foundation, then he/she is applying for a Visa extension. In that case, apply for extension, first, before leaving the Kingdom and re-entry.
By the way, all international airports in the Kingdom has immigration office that can handle re-entry. Password, photo, and cash is all you need.
I did TM30 three times, and each time is a bit different.
My first time was two years ago. I was three months late. Not days, not weeks, but months with a capital "M." I was fined for an amount. Not a big one. I was late because I didn't know I have to do TM30.
The second time around, I was much better. Going there in required time. Right then, I was told that the landlord was not required to appear if address is the same.
The third time was a bit odd. I came back late October, before the King's funeral. My superior told me to wait, both because of the work I have to do to catchup and the funeral. I was almost a month late but was not fined.
My experience with Thai immigration has been wonderful. If I show willingness to comply, the officers are willing to help. Having a superior who has experience in public sector also help.
I am quite happy to see your post. I have a single-entry non-immigration O visa as a volunteer as well.
About visa, you need to do a T.M. 30 within 24 hours of entering Thailand, and, before the expiration date, applied and have a work permit. Go to immigration office with your TM 30, work permit, and a report of what you have done in this time period, a report of the place you are volunteering for (IMPORTANT!! Do have someone capable of doing both report for you. The rule for what is required in the report changed couple of times last year. Do know what it is required.) and 1900 Baht. Go to your local immigration office early in the morning, get a cue, and wait for your turn. If everything is done properly, you will get a stamp that let you stay the first 30 days in a 90-day extension. In this 30-day, regional immigration office will send officers to verify your address, type of work, etc. At the last day of the first 30 days, go to local immigration office again to get the last 60 days stamp.
You will need to do the extension twice. (TM 30+work permit+reports+ 1900=30 day and 60 days.)
Before you do it the second last time, you also need to send report of your work and a report of you organization to local government. My place of work is in ChiangMai Province. Therefore, my reports went to the provincial government of ChiangMai. Before the end of ninth month, it will notify the immigration office if they are ok with you. If you do, at the end of ninth month, you will get a one year stamp.
1. I apply my non-O through a well connected agent.
2. The parts about photo, as in has to have 40 photos of you doing your job in a report is new. Not only that, the report also needs to indicate who else is in the photo, what you are doing, what date, what time, and where. The rumor is that some higher upper really like reports from a certain NGO, and therefore want everyone to do the same.
3. If someone needs to check up on you, they will come. The check is used to be conducted by local police department. Now, it's conducted by officers from regional HQ.
4. Generally speaking, if you didn't have all the documents ready, you're done. The only thing you can do, is do over.