Part 1: raise of body temp.
Yes you can raise you body temp at will, there are several ways of doing so.
The first way: aka the CAT
Cold anticipated thermogenesis, is probobly the first way you will feel the sensation of CAT(cold anticipated thermogenesis)
When an experienced Ice bath/swimmer takes off his clothes, and knows that he is soon going to take a swim, This is When CAT comes to visit.
The sensation is different for different people, but here are some ideas of what the CAT feels like.
Shivers down your spine,
Hands start sweating,
shortness of breath,
neck, face and upper back shivering.
So if you want to get the CAT, and you are an experienced Ice swimmer, Just think about your next swim and she will come crawling and stroking herself against your legs.
The Second way: aka CIMCA
The scientific name for this technique is, Cyclic Isometric muscle contraction and apnea, Lets call it CIMCA,
Proven in studies to raise body temperature, up to +2.5C, which is ALOT in body temp.
The temperature raise during CIMCA is probobly due to, Muscle activity combined with CO2 build up.