Hi Urva,

I'd say "no" to both questions, at least not without hard-to-maintain customizations even for the first point (if you need the message to only show up on Work plan pages). 

Feel free to submit Ideas for both these points.

For  validations too? Because I think in recent version of PPM there seems to be flexibility to update ootb validations.

indeed, we've made it very easy to customize some of the PPM validations in recent PPM versions, but we haven't covered validations from the work plan (yet). You can see customizable validations in file PPM_HOME/conf/validations/seed/validations.conf

Note however that we don't really make the validations customizable, we make it so that fields on the PPM screens can use different validations from the ones that are hard-coded in the product. The built-in validations are left untouched, we just allow you to use a different (custom) validation on specific field(s).

It's usually very easy for us to make an existing field validation customizable on a PPM screen, but the change has to be done on every screen where we want the validation of the field(s) to be customizable. Most importantly, the problem here is that we need to pass some extra context token to the Validation ([PROJECT_TYPE_ID], and possibly [PROJECT_ID] just in case), and this requires a lot more code changes on the work plan pages, so this isn't a tiny change at all.
For example, we recently modified the validation used on the "Specific Resource Requested" column of Staffing Profile to make it customizable and pass the resource pool id of position's selected resource pool to the validation as a token.