Dedicating a second time is usually merely a waste of your time. You might, for instance, if you had to do it on the astral the first time and now you are able to do it here. Another reason might be if you fucked up real bad the first time--or if there is any question of having done something totally wrong. Say, you got no blood on the paper the first time (and I am not referring to wimpy problems such as bumbling the recitation of prayer, using the "wrong" candle, paper not burning properly, not getting "enough" blood on the paper, etc.). Or, you were disrupted the first time--say, a fire alarm went off and you had to abandon the ritual the first time, or some idiot disrupted you. Then you might repeat it.
Notice that this is NOT a reverse ritual. Doing it twice is simple redundancy and, at most, a waste of time. A reverse ritual is when you wish to reverse the dedication and go back to being without. Generally I regard that as a waste of time, too--plus you WILL be abandoned by the Gods if you do that. For how long, we do not know--or how difficult it is to return. This is more serious than simply doing nothing. A reverse ritual means you are not sincere, or were not at the time you did your dedication. If you perform the ritual with the intent of leaving, it is usually going to end badly.
As for doing it accidentally or impetuously, I would not know. It would seem that there should be a safety mechanism to make it difficult to do a reverse ritual by mistake, since otherwise it would be quite simple for the enemy to do it on your behalf or somehow get you to do it, be abandoned by the Gods, and then usurp your energy. All without your input. And how common is that?
