Can deviation be possible on a choice statement?

YANG
1

a choice statement with three possible cases have been defined in a yang. I would like to restrict a particular case based on the value of another leaf in the yang.

2

Since deviation or deviate statement does not have condition (when statement) to check values in another leaves, I do not think it is possible to achieve it through deviation.

What you may try is to use augment, which can check values. E.g. from RFC8022

augment "/rt:routing-state/rt:ribs/rt:rib/rt:routes/rt:route" {
    when "../../rt:address-family = 'v4ur:ipv4-unicast'";
    description
      "This leaf augments an IPv4 unicast route.";
    leaf destination-prefix {
      type inet:ipv4-prefix;
      description
        "IPv4 destination prefix.";
    }
  }

So your augments might look like:

augment "path to choice" {
    when "condition1";
    case  mycase1 {
...
    }
  }

augment "path to choice" {
    when "condition2";
    case  mycase2 {
...
    }
  }