Adding a simple variant to a piece of clothing

I have a file (which is a vest) with 10 variants. The file name is:
mp_m_freemode_01_mp_m_january2016^task_011_u.ydd

And the variants are called:
mp_m_freemode_01_mp_m_january2016^task_diff_011_a_uni.ytd
mp_m_freemode_01_mp_m_january2016^task_diff_011_b_uni.ytd
mp_m_freemode_01_mp_m_january2016^task_diff_011_c_uni.ytd
And so on.

I changed one of the vests, and that works, but I wan’t to add a few vests, how do I make this work? I’ve simply copied one of the files, renamed it to the firs letter that was not in use, but I cannot select it in my server.
So the file I’ve added is called:
mp_m_freemode_01_mp_m_january2016^task_diff_011_k_uni.ytd

I also made sure to rename the texture file in openIV to the corresponding letter: task_diff_000_k_uni.png

I’ve read a lot of tutorials, but most of them are about streaming whole packs and seem complicated, I just want to add a few variants to existing clothing. Any idea on how I can manage this?