The wish spell enables you to emulate any spell of 8th level or lower.
Can a sorcerer apply a metamagic effect to the emulated spell by spending the appropriate number of sorcery points (provided that he knows said metamagic effect)?
For example, could he cast wish and spend sorcery points to use Extended Spell on his casting of death ward?
Wish states that you can use it to:
...duplicate the effect of any other spell of 8th level or lower. You don't need to meet the requirements of that spell, it simply takes effect.
Note that it doesn't say anything about the fact that you are casting the spell. You aren't. You are casting wish and as the effect, getting the effects of another spell.
The rules for metamagic say:
You can only use one Metamagic option on a spell when you cast it, unless otherwise noted.
And every metamagic option except empowered spell begins with:
When you cast a spell...
Thus, you could apply metamagic to wish, but it would only apply to the duration and other characteristics of wish itself (since that is what you are casting), not the spell whose effects it is duplicating. At the exact time of casting wish only has the characteristics (range, duration, etc.) listed for wish and not the spell it is duplicating.
This effectively means that you can only apply Quickened Spell and Subtle Spell to wish, neither of which will affect the duplicated spell's effects. The only effect would be to be able to cast wish itself as a bonus action and without somatic or verbal components respectively.
Empowered Spell says:
When you roll damage for a spell...
There are no other requirements than this, and this can clearly only be applied after the spell is cast and does not depend on having actually cast it. Thus, you can still empower any spell damage resulting from a wish-duplicated spell.
Another option would be of course simply to wish for a spell with its metamagic effects. However, this would be outside the realm of duplicating a spell and into the custom wish territory. Thus it would come with the 33% chance of never being able to cast wish again.
Jeremy Crawford appears to differ on this interpretation in this Tweet:
Q: Can you Twin a spell duplicated with Wish? And if you do, how many sorcery points do you use.
A: Yes, and use the number of points appropriate for the level of the spell you are duplicating.
And again in the Sage Advice Compendium:
Can my sorcerer use Twinned Spell on a spell duplicated by the casting of a wish spell? And if so, how many sorcery points does it cost? Yes, you can. It costs the number of sorcery points appropriate for the level of the spell you’re duplicating.
It isn't really clear what logic JC uses to support this answer. It is possible he is implying that wish does actually result in the duplicated effects being cast, but that does not appear to follow the RAW. This might also have an impact on other effects that depend on the spell being "cast". But, if it makes more sense to you and your DM/table prefers, this ruling is there to be used.
Despite the rules excluding Wish from being Twinned, due to its range of self, the Sage Advice Compendium explicitly confirms this:
Can my sorcerer use Twinned Spell on a spell duplicated by the casting of a wish spell? And if so, how many sorcery points does it cost?
Yes, you can. It costs the number of sorcery points appropriate for the level of the spell you’re duplicating.
This doesn't seem to fall under RaW, as Wish is described as
Wish
9th level conjuration
Casting Time: 1 action
Range: Self
And Twinned Spell requires:
When you cast a spell that targets only one creature and doesn’t have a range of self,
but apparently Wish is a special case. By Sage Advice, you can at least Twin or Empower a Wish-based spell. I would discuss with your DM what rulings he prefers to follow, and go from there.
You can't metamagic the Death Ward because you must cast the spell yourself to use metamagic. Most of the metamagic options explicitly say "when you cast a spell", and there's a general restriction that "you can use only one metamagic option on a spell when you cast it".
You also can't metamagic the Wish to increase its duration, because Extended requires the spell to have a duration of one minute, and Wish's duration is zero. (Similarly, Careful, for example, requires the spell to allow a saving throw to reduce damage, and Wish doesn't have one.)
(The argument could be made that when Wish duplicates another spell, it takes on that spell's properties including its duration. I would respond that you have to Extend the spell when you cast it, at which point it's still Wish.)
When you cast Wish you're saying "Hey, universe, gimme a Death Ward!" and it happens, because you're an umpteenth-level wizard and the universe does what you say. But that's not the same as creating the Death Ward yourself. You lose a little bit of control.
