Customize feature image in header blog for modern child

Sorry its not possible, the featured image uploaded in the post is only shown here.  

You can customize your theme using the blank child theme in your website.

If you want to hide one of the image then please share the page url to provide you the custom css for that.  

You are using the modern theme and you want o change the header only on blog and single post page. This is not possible the header is changed throughout the website. If you want the header same as childone theme then you need to use the childone theme instead of modern theme. You can download the childone theme from the wplms package from themeforest and upload it to your theme directory and activate it. NOTE: When you switch the theme then some widgets and customizer setting will change, therefore you have to manually add the widgets in the sidebar and do the customizer settings accordingly.

There is no migration code, you have to switch the theme if you want.  

For RTL you can simply select the site language to some rtl language the wordpress will automatically change the website to rtl. OR you can use the rtl plugin it will change your website in rtl.