This needs knowledge of your map and what you use in other triggers. If you have a variable pointing to that Hero, you need to re-direct it after replacement. I can write it in JASS (only simple JASS, I don't use NewGen, if you know what is it
). Let udg_Heroes be an array of Heroes on the map (in editor you type 'Heroes' as var name, udg stands for user-defined globals), and one of them uses such artifact, and global integer udg_NumberOfHeroes (also simply NumberOfHeroes) displays the maximal possible quantity of Heroes in the array (can be larger than really used). If you don't use such variables, just create unit array Heroes and integer var NumberOfHeroes with start value 0. Here's what you need.
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Text1.txt should be copied to the pre-script (in trigger editor, click the uppest line in the left window, it must contain the name of the map, and then, in the lower-right window, you have place for the pre-script. Insert this here.) Text2.txt is the text of the trigger named ItemConspirationActivated (you have to create such trigger, convert it to text through the Edit menu and replace all its text with my code in text2.txt).
But, that's not all. Create a dummy item type which would never be used, and replace 'I000' in text1.txt with its ID (lines 50 and 56, or just Ctrl+H in Notepad). It would be really 'I000' if this dummy item is the first non-standard item on the map. In text2.txt, instead of 'AIil' (line 2) use the ID of ability which creates illusions (in object editor, press Ctrl+D to see IDs instead of names). Replace 'will' (line 8) with item ID of the item that gives the ability (damn the instant cast, wc3 hasn't enough time to spend a charge of the item). And, also in text2.txt, where it is TriggerSleepAction(5.00), replace 5.00 with the time the spell works (in seconds).
Huh. Must work. But, if your Hero has additional abilities added through triggers, you need to add them again when it is cast.
P. S. Must work even if you cast the ability next time while being affected with previous cast. Rep me please if it works.
P. P. S. If you need anything else to be jassed, ask me.