Yes, it is the same as temporary appointment! Is that something people mention? I changed things a bit and wrote:
"This is to certify that XYZ was part of my research team as a full-time Research Technician from 5th May, 2017 up to 6th October, 2017." Is that sufficient?
Or should I say, "
"This is to certify that XYZ was part of my research team as a temporary, full-time Research Technician from 5th May, 2017 up to 6th October, 2017."
I don't think you need to add the word "temporary". For mine, my employer wrote "this is to confirm the employment of xxx at xxx. She was employed full-time in the position of xxx. She worked 37.5 hours per week, wage was xxx". And my letter was accepted and approved.