No, or at least with ice (snow)
After read the SJuan76 and kingledion you can notice that it's almost impossible get colder the planet using comets. A comet has very low water compared to the entire oceans so the change of temperature they do is impercetible.
Also, you can't cold directly the planet making ice because to cold an object you have to warm another (transfer heat). Maybe you could transform thermal energy into electricity but that can't be done at planetary scale.
But....
What if we freeze water in order to prevent future heat and not to reduce the actual heat?
Before continue I have to say:
- This obviusly can't be done at planetary scale, or at least with our technology.
- We won't use ice. I hope you won't mind. Well, we can but it would be better not.
Do you have read about the Albedo? Well, you should do.
Albedo (/ælˈbiːdoʊ/) is a measure for reflectance or optical brightness (Latin albedo, "whiteness") of a surface. It is dimensionless and measured on a scale from zero (corresponding to a black body that absorbs all incident radiation) to one (corresponding to a white body that reflects all incident radiation).
Each material has and albedo value:

With this we can know that some materials reflect better the light of the sun (heat) and it escape of the Earth.
I've found some values over the Internet. I'm not sure which of them is more precise so I'll use all of them:
$$\begin{array}{|c|c|}
\hline
\ \text{Sustance} & \text{Albedo}
\\ \hline
\ \text{Ocean} & \text{%}5 - 10\text{%}
\\ \hline
\ \text{Open Ocean} & 6\text{%}
\\ \hline
\ \text{Melting Snow} & 40\text{%}
\\ \hline
\ \text{Oceanic Ice} & 50\text{%} - 70\text{%}
\\ \hline
\ \text{Atartica Snow} & 80\text{%}
\\ \hline
\ \text{Fresh Snow} & 80\text{%} - 86\text{%}
\\ \hline
\ \text{Freshly Fallen Snow} & 90\text{%}
\\ \hline
\end{array}$$
Firt we have to know the actual heat that it's absorbed by oceans, and the amount that it's reflected.
$$\frac{\text{Ocean surface}}{\text{Earth surface}} = \text{% of ocean surface}$$
$$\frac{361,000,000 \text{ km²}}{510,072,000 \text{ km²}} = 70.77 \text{%}$$
So the $70.77 \text{%}$ of the Earth surface is cover by water.
We know that solar constant of light in the atmosphere is $1,366 \text{W/m²}$ but at the surface only reach $1,025 \text{W/m²}$ (I won't count clouds).
So:
$$361,000,000 \text{ km²} \times 1,025 \text{ W/m²} = 370,025,000,000,000 \text{ Watts} = 370.025 \text{ TW}$$
If we substract the values of the albedo (that power * albedo value) with the total energy we can know how much energy is absorbed and how much is reflected:
$$\begin{array}{|c|r|r|r|}
\hline
\ \text{Sustance} & \text{Albedo} & \text{Reflected} & \text{Absorbed (Heat)}
\\ \hline
\ \text{Ocean} & 5\text{%} & 18,501.25\text{ GW} & 351,523.75\text{ GW}
\\ \hline
\ \text{""}& 10\text{%} & 37,002.50\text{ GW} & 347,823.50\text{ GW}
\\ \hline
\ \text{Open Ocean} & 6\text{%} & 22,201.50\text{ GW} & 347,823.50\text{ GW}
\\ \hline
\ \text{Melting Snow} & 40\text{%} & 148,010.00\text{ GW} & 222,015.00\text{ GW}
\\ \hline
\ \text{Oceanic Ice} & 50\text{%} & 185,012.50\text{ GW} & 185,012.50\text{ GW}
\\ \hline
\ \text{""} & 70\text{%} & 259,017.50\text{ GW} & 111,007.50\text{ GW}
\\ \hline
\ \text{Atartica Snow} & 80\text{%} & 296,020.00\text{ GW} & 74,005.00\text{ GW}
\\ \hline
\ \text{Fresh Snow} & 80\text{%} & 296,020.00\text{ GW} & 74,005.00\text{ GW}
\\ \hline
\ \text{""} & 86\text{%} & 318,221.50\text{ GW} & 51,803.50\text{ GW}
\\ \hline
\ \text{Freshly Fallen Snow} & 90\text{%} & 333,022.50\text{ GW} & 37.002,50\text{ GW}
\\ \hline
\end{array}$$
Water is about $70.77 \text{%}$ of the surface of Earth, now is your mission determine if changing the albedo of that surface (turn water into ice or snow) would reduce Significantly the heat of Earth. I think yes.
I am not sure but I think human contamination increase the amount of energy aborbed by $+0.2 \text{ W/m²}$, with a range $+0.1\text{ W/m²}$ to $+0.4 \text{ W/m²}$.
So human contribute with $102,014.4\text{ GW}$, with a range of $51,007.2 \text{ GW}$ to $20,402.88 \text{ GW}$. If you freeze the oceans the new albedo gain would counter-act our actual contamination.