Could you be a little more specific as to what it is you’re asking? I currently see your question as multifaceted
- How difficult is it for a Catholic to undergo all the motions of conversion to Mormonism (i.e. the actual steps of initiation)?
In this case, it’s very easy to convert to Mormonism. The LDS missionaries only have six discussions with a potential convert concerning LDS doctrine, and the meatier doctrines aren’t taught in these discussions. A potential convert is asked if (s)he would like to be baptized only by the second discussion. If the investigator answers yes, a baptism can be scheduled within the week and the recently baptized can be confirmed the very next day. Compare this to the Catholic modus for conversion which includes a 9 month course called R.C.I.A. Study of more than just the basic creeds and dogma of the Church.
- How difficult is it for a Catholic to adopt LDS beliefs and/or discard previously held Catholic beliefs?
The answer to this will obviously be relative to the exact person in question. What if the person was a committed, believing Catholic when the LDS missionaries met him or her? I would suspect that the time to switch beliefs would take a relatively long time, whereas the case of an already lapsed Catholic meeting missionaries would likely take far less time. My own conversion went in the opposite direction (from Mormonism to Catholicism). I had already lost faith in the religion of my ancestors prior to ever considering Catholicism, so there wasn’t any doctrinal baggage that I had to deal with. Furthermore I already had intensely studied Catholicism on my own for nearly 3 years prior to approaching R.C.I.A. so I was already certain of my allegiance to the Catholic Church prior to even converting. It’s certainly conceivable that there are Catholic-turned-Mormons out there who were in a similar boat as I: They stopped believing in Catholic teachings prior to finding Mormonism and even gained a testimony of the Book of Mormon and the LDS Church prior to ever once meeting a missionary or ever stepping foot in an LDS meetinghouse.
- How difficult is it for a Catholic to deal with the break in previous associations due to conversion to the LDS Church?
Again, this will depend on the individual. I would imagine that a person raised in a devoutly and culturally Catholic family such as an Italian, Filipino, or Irish one would have to deal with a great deal of familial guilt for converting, just as us 6th generation Mormons from pioneer stock have to deal with when we leave the LDS faith for another. An individual who was raised in a nominally Catholic household (just as an individual raised in a Jack Mormon home) would likely experience minimal friction.
So to answer your question:
It all depends!