Modtweaker's Thaumcraft integration extends IItemStacks.
That means that you can use the methods below on any IItemStack object:

You can use this to override what aspects an item would normally have.
Requires a CTAspectStack[] or many CTAspectStack objects.

ZenScript
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<minecraft:stone>.setAspects(<aspect:ignis>*5);

You can use this to prevent certain aspects from being added to an item.
Requires a CTAspectStack[] or many CTAspectStack objects.

ZenScript
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<minecraft:iron_ore>.removeAspects(<aspect:terra>);