That is cool! I think I’ll use that.
Tsuzuki,
The reason one can not belong to two different religions simultaneously is not about the things they hold in common. Rather, it is about their beliefs that contradict. When one embraces a religion one assents to its doctrine, its moral teaching, its ideas of spiritual matters, things we can not see, such as an afterlife.
We can try to harmonize teachings of different religions that are incompatible, but that is impossible. For example only, if one religion says that it is sinful to consume alcohol and another says it is a holy thing to do, both can not be true. If one religion says taking heroin as a sacrament is good, and another says injecting heroin is evil, both can not be true. If a religion says ritual suicide pleases God, and another says it is evil and God forbids it, both can not be true, unless the two have different Gods. In that case you have to choose which God you will follow, or neither. You can not follow both. You can not commit suicide and not commit suicide. When you come to a fork in the road you can not take two paths, left and right, north and south. You must choose one.
The doctrines of Mormonism and Catholicism are incompatible. There is either a triune God or there is not. Jesus is either a divine person, the second person of the Holy Trinity or He is a created being. If one says it does not matter which is true then one should neither be a Mormon or Catholic, because each religion says this is essential to their belief.
One can not be a Methodist and a Calvinist, and a Catholic, and animist, pagan, Mormon, Jew, atheist, pantheist, all at the same time. For the same reason one can not be any two of these at the same time.
In the very early days of Christianity the idea arose that there was some truth in all religions. This is indeed true, but the idea was that all religions could therefore be melded into one. This was called syncretism. It was condemned by the Catholic Church as heresy, a false belief. Either all religions can be harmonized or they can not. If they can and the Catholic Church is wrong about it, or that is what you think, then be a syncretist, or pagan, or a nothing. Don’t be a Catholic or try to be, because you reject the teachings of Catholicism. You can not sincerely be both. If you reject the teaching of a religion and try to belong to that religion it makes no sense and it makes you a hipocrit.
If you like or believe some of the teachings of Catholicism and reject others, then continue to look for a religion that aligns with what you believe, or start your own. Many people do that in our confused time. Maybe you can pick the doctrines of Catholicism you accept and certain Mormon doctrines where you do not believe the Catholic position and come up with a hybrid religion. It will not be Catholic, or Mormon. It will be Tzusukan.
Best wishes.