I have an MSBuild script which compiles my existing solution but I\'d like to change some properties of one of the projects within the solution at compile-time, inc
You're on the right track with the MSBuild Extension Pack.
I find the easiest way to conditionally generate the assembly details at build time is to add an "AssemblyVersion" target directly to my .csproj file(s) that require an updated AssemblyInfo file. You can add the target directly to each csproj file that requires an updated AssemblyInfo file, or as I prefer to do it, create a custom targets file with the AssemblyVersion target and have each csproj file include your custom targets file.
Either way you likely want to use the MSBuild Extension Pack or the MSBuild Community Tasks to use their respective AssemblyInfo task.
Here's some code from our build scripts:
AssemblyVersion;
$(BuildDependsOn)