How to add an if statement to a struct initialization

I'm trying to add an if statement in a nested struct, and whenever I try to build I get: syntax error: unexpected if, expecting expression.

I've found a simple code that shows what i'm trying to do:

package main

import "fmt"

type Salary struct {
    Basic, HRA, TA float64
}

type Employee struct {
    FirstName, LastName, Email string
    Age                        int
    MonthlySalary              []Salary
}

func main() {
    e := Employee{
        FirstName: "Mark",
        LastName:  "Jones",
        Email:     "mark@gmail.com",
        Age:       25,
        MonthlySalary: []Salary{
            Salary{
                Basic: 15000.00,
                HRA:   5000.00,
                TA:    2000.00,
            },
            Salary{          //i want to add a condition "if true" then add this salary struct
                Basic: 16000.00,
                HRA:   5000.00,
                TA:    2100.00,
            },                // till here
            Salary{
                Basic: 17000.00,
                HRA:   5000.00,
                TA:    2200.00,
            },
        },
    }

And I found that this might be done through preprocessor, which I'm totally clueless about.

Please note that the struct is imported from another package on my original code and I can't change the way it's declared and used.