What is the ruling regarding spots found on underwear resulting from prostate congestion, and do they take the same ruling as urine? Is it obligatory to change or wash the clothes whenever these spots are found? Does the ruling concerning those with urinary incontinence apply to me, which necessitates performing ablution at the beginning of the time for each prayer?

Purifying clothes is obligatory upon seeing spots emanating from the private parts. If you are unable to remove them, there is no blame. It is obligatory to place a tissue or similar on the organ to prevent the spread of impurity. As for ablution, if you are excused due to incontinence, you perform ablution for each prayer after taking precautions to prevent the spread of impurity, and you pray the obligatory and supererogatory prayers. If you are able to pray with a valid state of purity, then that is what is obligatory.