You should not. Windows registry is not meant to become a file repository. Stuffing huge data contents in there will have a terrible impact on the performance of the system.
You might consider the proper solution instead: using a folder in application data folder (or local application data folder) of logged in user.
Something like:
using System;
using System.IO;
using System.Reflection;
string path = Path.Combine
(
Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
Assembly.GetExecutingAssembly().GetName().Name,
"temp"
);
string path = Path.Combine
(
Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
Assembly.GetExecutingAssembly().GetName().Name,
"temp"
);