Redactor as default WYSIWYG in 5.6?

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Hi,

I have been developing a church website in 5.6 for a year or so now. The only real problem we've had is the ease of use of the WYSIWYG editor (We have a lot of older contributors on our site).
Redactor seems to be the way to go, and it has proved useful on the beta site we've started testing on. However, in order to get it, we must upgrade to 5.7 - However, doing that would require re-purchasing our theme and add-ons (since the developers are not supporting upgrades for 5.6 to 5.7). We just don't have that type of money in our budget.

Is there any way to integrate Redactor into 5.6.3 as the default editor instead of TinyMCE?

Thanks