Some quick research confirms RAW although whomever writes the metamagic version down must have the prerequisite feats, the subsequent users of the scroll do not per RAW and must only make a Spellcraft(DC 15 +spell level, -2 if within their specialty school) to copy it into their spellbook, where it’s a spell of whatever level the metamagic increased it to.
Regarding your example, a wizard using Elemental Spell(+1) to change a Fireball(SL3) to do Cold damage would know the altered version as a 4th level spell they could either cast or write down.
Someone else finding the scroll could transfer it to their own spellbook with a successful Spellcraft(19) check; from which they could memorize/cast it like any other 4th level spell they know. However it will only do Cold damage unless they know Elemental Spell to rechange it.
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<source:
www.d20pfsrd.com; I bolded relevant sentences>
Scribe Scroll (Item Creation)
You can create magic scrolls.
Prerequisite: Caster level 1st.
Benefit:
You can create a scroll of any spell that you know. Scribing a scroll takes 2 hours if its base price is 250 gp or less, otherwise scribing a scroll takes 1 day for each 1,000 gp in its base price. To scribe a scroll, you must use up raw materials costing half of this base price.
See magic item creation rules for more information.
Magic Items and Metamagic Spells:
With the right item creation feat,
you can store a metamagic version of a spell in a scroll, potion, or wand. Level limits for potions and wands apply to the spell’s higher spell level (after the application of the metamagic feat).
A character doesn’t need the metamagic feat to activate an item storing a metamagic version of a spell.
Sidebox faq: At what spell level does a spell modified by a metamagic feat count for purposes of concentration DCs, magus spell recall, or a pearl of power?
The spell counts as the level of the spell slot necessary to cast it.
For example, an empowered burning hands uses a 3rd-level spell slot, counts as a 3rd-level spell for making concentration checks, counts as a 3rd-level spell for a magus’s spell recall or a pearl of power.
Spells Copied from Another’s Spellbook or a Scroll
A wizard can also add a spell to his book whenever he encounters one on a magic scroll or in another wizard’s spellbook. No matter what the spell’s source, the wizard must first decipher the magical writing (see Arcane Magical Writings). Next, he must spend 1 hour studying the spell. At the end of the hour,
he must make a Spellcraft check (DC 15 + spell’s level). A wizard who has specialized in a school of spells gains a +2 bonus on the Spellcraft check if the new spell is from his specialty school. If the check succeeds, the wizard understands the spell and can copy it into his spellbook (see Writing a New Spell into a Spellbook). The process leaves a spellbook that was copied from unharmed, but a spell successfully copied from a magic scroll disappears from the parchment.
If the check fails, the wizard cannot understand or copy the spell. He cannot attempt to learn or copy that spell again until one week has passed. If the spell was from a scroll, a failed Spellcraft check does not cause the spell to vanish.
