Will Propecia cause accelerated hair loss if you try it, then stop taking it after a period of time?

Propecia is not meant to treat Diffuse Pattern Alopecia so you need to rethink what you are doing and clarify things with your doctor.  Propecia also does not cause accelerated hair loss.  If it does, people will not take it for hair loss.

Studies do not support the statement that a person taking finasteride will be worse off than having never taken it. This statement is not supported by any of the clinical studies taken to date. However, users must keep in mind:the drug must be used foreverone might experience shedding in the first 1-3 monthsonce a patient stops, any newly gained benefits will be lost in 9-12 monthsif one takes for 5-10 years and then stops, they may look much more bald than on day 1 (starting day) because they hair loss will 'catch up' to what it would have been if the drug were not used.

Propecia is a great drug (the only FDA approved oral drug) that
really works for male pattern balding. But it doesn’t always completely
stop the balding process. Your genetic predisposition will eventually
win out. Some men do have great long term effects. The sexual side
effect of libido or erection associated with Propecia is about 1 to 2
percent and after 10+ years of use it’s hard to imagine that one might
start having the side effects of the drug after 10 years. (But it is
possible) More probable is that men in their late 40’s would likely
have issues with libido and erection due to their age. If you are on Propecia and you stop it, there will be no effect on your permanent hair that is not genetically impaired. Any benefits of the drug will cease and after stopping the drug you will lose all of the benefits in what I call "catch up hair loss' which means that you will revert to what would normally have happened had you never taken the drug.