Just put the rule `0^0 := 1' into EvalRules. For example,
before making this definition we have:
2: [-2, -1, 0, 1, 2] 1: [1, 1, 0^0, 1, 1]
1: 0 .
.
v x 5 RET 3 - 0 V M ^
But then:
2: [-2, -1, 0, 1, 2] 1: [1, 1, 1, 1, 1]
1: 0 .
.
U ' 0^0:=1 RET s t EvalRules RET V M ^
Perhaps more surprisingly, this rule still works with infinite mode
turned on. Calc tries EvalRules before any built-in rules for
a function. This allows you to override the default behavior of any
Calc feature: Even though Calc now wants to evaluate 0^0 to
nan, your rule gets there first and evaluates it to 1 instead.
Just for kicks, try adding the rule 2+3 := 6 to EvalRules.
What happens? (Be sure to remove this rule afterward, or you might get
a nasty surprise when you use Calc to balance your checkbook!)