This mystic text is the reverse of the Libram of Ineffable Damnation, greatly beneficial to Good magic-users, most baneful to non-Good ones. 

Like all magical works of this sort, it vanishes after 1 week of study, and the character having benefited from it can never be so aided again.

Libram of Ineffable Damnation. This work is exactly like the Libram of Gainful Conjuration except that it benefits Evil magic-users, and non-Evil characters of that class will lose 1 level of experience merely from looking inside of its brass-bound covers, in addition to the other ill effects of perusing but 1 line of its contents.

Libram of Gainful Conjuration. This mystic compilation contains much arcane knowledge for magic-users (including illusionists) of Neutral (Neutral, Chaotic Neutral, Lawful Neutral) alignment. 

If a character of this class and alignment spends a full week, cloistered and undisturbed, pondering its contents, he or she will gain experience points sufficient to place him or her exactly at the mid-point of the next higher level. When this occurs, the libram will disappear—totally gone— and that same character can never benefit again from reading such a work. 

Any non-Neutral magic-user reading so much as a line of the libram will take 5-20 points of damage, be unconscious for a like number of turns, and must seek a cleric to atone in order to regain the ability to progress in experience (until doing so, he or she will gain no further experience). 

Any non-magic-user perusing the work will be required to save versus magic in order to avoid insanity. Those characters going insane must receive a remove curse and rest for 1 month or have a cleric heal them.

Special Note. All magical books, librams, manuals, tomes, etc. appear to be "normal" works of arcane lore. Each is completely indistinguishable from the other by visual examination of the outer parts or by detection for magic aura. 

Bard characters will have normal chances of finding out the nature of such writings, as will an identify spell from a magic-user. 

Otherwise, only a wish will be useful in typing a magical writing, i.e. alter reality, commune, contact higher planes, limited wish, true seeing, true sight, and other spells or powers are useless. 

A wish will reveal general contents of a book, telling what characteristics or class is most affected (not necessarily benefited) by the work. It requires a second wish to determine exact contents. 

After being perused by a character, most of these magical works will vanish forever, but those which are non-beneficial to the reader will typically be attached to the character, and he or she will be unable to be rid of it. 

If the work benefits another alignment of character, the possessor is geased to conceal and guard the writing. 

As Dungeon Master you should use your judgment and imagination as to exactly how these items will be treated, using the rules herein as parameters.