How to pass custom parameter a value

I developed an item template whos's located in: 
> C:\..\..\Documents\Visual Studio 2017\Templates\ItemTemplates

On my code i'm using `AddFromTemplate()` method to load my item template. The item template has a `$CustomParameter$` but i dont want to pass the value in the `vstemplate` file. I want to pass a value from my code.

I'm trying to use `replacementsDictionary.Add("$CustomParameter$", "WhatIwant")` but this not working because the item it's not on my solution. But if i use this:

    <CustomParameters>  
        <CustomParameter Name="$CustomParameter$" Value=""/>  
    </CustomParameters> 

 
 on the vstemplate located in the folder above it works well but i can pass the value who i want.

Any suggestion?

Source: 
https://msdn.microsoft.com/en-us/library/ms185301.aspx; 
https://msdn.microsoft.com/en-us/library/0c672h41.aspx