yes to the first question, and no to the second. What I did was allocate 100% of special and bonus pays to TSP, and then when I deployed, I didn't have to change anything - I was getting way more bonus and special pay and it took care of itself. Come W2 time, all the TSP contributions during a deployed time showed up appropriately, and were definitely above the standard annual limit.
The only time I had an issue was when I deployed during the last week of Dec one year and my TSP didn't kick in, since that month had already closed out in DFAS' mind and I had already maxed out my annual contribution limit in Nov.