I have created a couple of entries and buttons in XAML (no C# code yet).
Is it possible to edit or even add elements in C# code to a StackLayout which was made in XAML?

For example, having the following XAML code:

```
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:local="clr-namespace:ORTEC_MOBILE"
         x:Class="ORTEC_MOBILE.MainPage"
         BackgroundColor="#0074ff">

<RelativeLayout>
    <StackLayout HorizontalOptions="FillAndExpand"
        RelativeLayout.YConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height, Factor=0.25,Constant=0}"        
        RelativeLayout.WidthConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width,Factor=1,Constant=0}">
        <Label Text="Login" FontSize="36" TextColor="White" HorizontalTextAlignment="Center">
        </Label>
        <Label Text="Welcome back! Please log into your account." FontSize="12" TextColor="White" HorizontalTextAlignment="Center">
        </Label>
    </StackLayout>
</RelativeLayout>

```

Is it possible to add a button to the layout using C# code?