Asking for "any desired form" probably doesn't have an answer.
Asking it to group by exponents is more feasible.
I believe this will accomplish that
f[x_] := (E^(-h k0 x) + E^(h k0 x)) (-(-1 + 1/4 E^(-h (n1 + n2) x) (1 + E^(2 h n1 x)) (1 + E^(
2 h n2 x))) m1 m2 (-2 Z13 + m1 n1 Z33 + m2 n2 Z33) - 1/4 E^(-h (n1 + n2) x) (-1 + E^(2 h n1 x)
)(-1 + E^(2 h n2 x)) (m2^2 Z13 - m1 m2^2 n1 Z33 + m1^2 (Z13 - m2 n2 Z33)));
Expand[f[x]] //. a_*Exp[c_]+b_*Exp[c_] :> (a+b)*Exp[c]