Will Visual Studio choke on customized .csproj files?
For example, I wanted to add a Target to update the version number in all AssemblyInfo.cs files. I plan to invoke this from the command line with MSbuild.
As another example, I would like to include the build timestamp into the compile, like so. This would be a pre-compile step (I guess), and unlike the example above, this one would run from within a build inside Visual Studio.
Will VS be ok with this?
Yes it does allow customizations. We integrated FxCop with our release-mode builds this way.
It will complain when you first load the project file after it's been edited, saying "it's been tampered with, do you wish to continue loading?" Just hit yes and continue on your merry way. It also lets you check a box to ignore the rest of the projects in the solution for the same warning.
As long as the code is a valid MSBuild extension, Visual Studio should be able to handle it. Under the hood the project files are really just MSBuild files and MSBuild does the dirty work of the VS build system. So as long as the file remains a valid MSBuild file it should be just fine.