Spell and Item Magic Resistance

[Tellus]

@GiedStephen

Hi, I have a question.

Imagine the situation: I cast a CrHe spell to make a oak chair appear. Some time after that, I get tired of the chair and want to change it into ash. So I cast an MuHe spell to change the kynd of wood. The point is: Does the first spell have any Magical Resistance against the second?

No

And then there're some associated questions about the topic:

If the caster of the first spell is a magic item, it makes any difference?

no

If normally the spell has some Magic Resistance, can you change it during the casting, lowering it?

irrelevant (but see below)

Is it different if both spells are casted by the same mage or a different one?

No (but see below)

Well, tthat's it. If there's some place in the rulebooks where explains about it, or you know or use some specific rules, please help me

Spells do not impart magic resistance (there's a topic about enchanted items having resistance here).

NB! If you wish to use MuVi on another wizard's spells as they are cast, you must exceed his penetration with your own (box on ArM5 p. 159).
The original caster can use forceless casting (penetration == 0) to make this easier for you.