score:3
You asked how to request that a different ECO be assigned to your next application. Some consulates do this by default (e.g., Russia), some do not (e.g., Nairobi) but I don't know the policy at Riyadh. So to be sure, you can use the following steps...
You asked if a certified translation should be accompanied with an apostille. If it is a legal document, yes.
You asked if you should resubmit an invitation letter if they already have one from your previous application. Yes, you should. A fresh application starts from square 1 and makes no assumptions about what they already have or do not have. You also asked what to do if your plans have changed wildly since your previous application. You should state your new plans honestly, and if they are wildly out-of-sync with your previous plans you can make a BRIEF statement in Part 9 of the application.