This section deals with duplication of permanent spells: apparently you're not supposed to do it. Casting a particular spell on a particular object, and then casting the same spell on the same object again - with the same or different parameters, it doesn't seem to matter much - will usually lead to effects you didn't anticipate, and it is always better to either disenchant the subject before the second casting, or find two different spells that you can combine to get the desired result. Even casting two separate permanent spells on a single person or thing can be tricky, but unlike the same spell twice, it isn't a near-guarantee of disaster.
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This section deals with duplication of permanent spells: apparently you're not supposed to do it. Casting a particular spell on a particular object, and then casting the same spell on the same object again - with the same or different parameters, it doesn't seem to matter much - will usually lead to effects you didn't anticipate, and it is always better to either disenchant the subject before the second casting, or find two different spells that you can combine to get the desired result. Even casting two separate permanent spells on a single person or thing can be tricky, but unlike the same spell twice, it isn't a near-guarantee of disaster.