Hello,
1. These strings can be changed via translation files, for example, https://prnt.sc/jtx20m > http://prntscr.com/jtx3d6
https://www.8theme.com/documentation/xstore/theme-translation/base-theme-translation/ (this article for xstore theme, but for royal it works in same way)
There is no option for the background, but you may use custom css code (Theme Options > Custom css):
.modal-dialog.text-center {
background-image: url(https://8theme.b-cdn.net/wp-content/uploads/2015/05/NewsletterImg.png);
background-size: cover;
background-repeat: no-repeat;
}
2. I am glad that you sorted out.
Regards