Can I use .NET Reflector to modify & recompile the code quickly?

.NET Reflector cannot do this, but other tools can decompile .NET assemblies, for example FileDisassembler (an add-in for .NET Reflector).

You can probably use the Reflexil add-in for Reflector to do that:

Reflexil is an assembly editor and runs as a plug-in for Reflector. Using Mono.Cecil, Reflexil is able to manipulate IL code and save the modified assemblies to disk. Reflexil also supports 'on the fly' C# and VB.NET code injection.

It's possible with .Net reflector along with reflexil. First download reflexiil and then open .net relector and load the reflexil into it using View->addins->select the reflexil file(all dlls) and then load. After that open the required dll file and go to tools->select reflectil, open the code and identify the required item, then edit..give to the assemblyy and select save as to save it to new file