[Avodah] Hamelech Hakadosh - during the year

[Sholom Simon]

>> ... if after Yom Kippur one uses Hamelech in place
>> of Hakel, the tefillah is equally invalid.
>
> I have been unable to find a source to either confirm or contradict this.
> Does anyone know of a source which speaks of this situation, i.e., if one
> says "HaMelech Hakadosh" at a time OTHER than the Aseres Ymei Teshuva?

I was reading "Shloshim Yom Kodem HaChag" and he says the same thing. 
Actually, he gave a broader rule -- any change that you make during the 10
days that are not specifically related to R"H/Y"K (e.g., things that
mention writing or sealing, etc. -- e.g., HaMelech) does not invalidate a
tefilla for after the 10 days.

But, alas, a quick look back, and I can't find it.

-- Sholom