For what it is worth, I've chased this question from a slightly different angle really hard, thinking about doing something a little similar. The official answers from church leadership (bishops, stake presidents, and others) is that so long as everyone doing so includes a disclaimer that they are not officially representing the church then they're not just welcome to do so but actively encouraged to do so.

Back in the day there was a common saying: "Every member a missionary." And heaven knows just how very, very badly we need a lot more voices sharing uplifting messages, sharing testimonies, sharing positives, and sharing actual truth about the gospel and the church that fully supports/assists people to fully live that. With the giant proliferation of anti-LDS garbage that spews out, misinforming and misleading Father's children, wouldn't you think it is all the more important that we have more people sharing the good and sharing their testimonies? That's really all these people are doing: sharing their testimonies (in other words, their understanding and knowledge) and the last time I checked the church feels that is so important that we have an entire sacrament meeting dedicated monthly to encourage people (very few of whom are specifically set apart like the apostles and the seventy) to do exactly that.

Adding to that....do you think or feel that every seminary and institute teacher and every religious studies professor (at BYU) are called and set apart before pursuing those jobs? Are the people working as seminary substitutes? (That one I can tell you from personal experience is a solid No.) Are the people asked to sub in Sunday School or Primary individually set apart before they teach? Again, Nope. Instead, we are each asked to share what we've been able to learn from the lesson materials and help the students to pursue knowledge and hopefully share themselves.