I would like to ask what the best approach would be in the following scenario. I have a project with all the tasks. I've created the baseline but my boss comes and says: I need you to add these other tasks (let's say 10 more tasks). How can I add those tasks to the existing baseline or should I create and save a new baseline?
Different scenarios yield a different answer, and even each scenario could have caveats where another answer might be better. If the project is about building a tangible product, adding and deleting tasks can occur all day long without change orders but also with out a baseline change. They just produce variances that you need to track and control. There are caveats to this, however, and some that come to mind are with the type of contract that is in place. For example, a seller may have added a stop loss clause in the level of effort required to produce the product, in which case adding two activities could exceed that threshold. Then a formal change, adding budget, and a new baseline are appropriate. So to answer your question definitively, you need to describe the specifics. I'll add to my answer once those specifics are known.
From a strictly mechanical viewpoint, if you are forced to make changes tot he baseline, then I would create a new baseline from that point forward. If you are using a tool, say MS Project, then you can preserve the original baseline to latter use to instruct upper management on the impact of the additional tasks and the changes to the cost and schedule to the project. If you are using EVM, I believe you would be forced to re-baseline, but again I would keep the historical baseline to get management buy in in the future for setting and sticking to the scope. On the other hand, if the new tasking is vital and obviously important to the whole of the project, then re-baselining as new is likely the way to go once management concurs with the new schedule and cost.
I recommend to review the additional tasks to determine if these will impact your project, such as your milestone dates or project costs. If there is an impact to your existing project schedule or budget, I would seek sponsor/business owner approval for the changes requests and re-baseline the entire project accordingly. If the additional tasks can be done without impacting the key milestones or budget, I would add the new tasks and just re-baseline only the new tasks (In MS-Project 2010, use “Project..Set Baseline..Set Baseline..For..click Selected Tasks”).
I have used the “Selected Tasks” re-baseline feature in MS-Project several times. For example, consider a new floor build-out. The project includes deployment for all IT components for a new office floor. If a change request comes in to add a conference room, I can add those new tasks to the project schedule without impacting existing project plans and schedule for the current scope. Of course, the change request needs to be approved and project cost updated accordingly.
You have a baseline of what? The Product Breakdown Structure (PBS) or the Work Breakdown Structure (WBS) or both? Adding tasks sound for me like extending scope, in this case work scope which need further efford and therefore money. If you just update your work packages structure by rearaning your tasks may not have an impact on scope.
Nevertheless any change lead to an update of the baseline and should be managed by a Change Control Board with the clear intension to communicate who have to do what.
It is unclear from your question these new tasks needs to be added because of what reason. Still if I were you I will create a new baseline if this is increasing my scope of work and subsequently the time.
If the tasks are breakdown of your already present activities with no change to scope then you can add it to the current baseline itself
In fact the answer is: it depends. On what?: You do not need to change scope to take baseline but if it does change you have to. Baseline is normally link to scope but in real life it's not so simple. If you want to track correctly your project you might want to baseline the new activities without re-baseline the old ones. If you have a really tight project with a lot of activities (hundreds) and a solid project management support by your company you'll prefer to not do a baseline on those activities if they do not change the scope.
And depending the software you use, it could give you some opportunities with this situation.
In theory, the project baseline is a snapshot of what was approved as the final plan. You should not add or removed baselined tasks as again "in theory" only an approved change request could rebaseline the project.
My 2 cents...
Add the tasks, link/sequence it properly and check the impact to the critical path. If it increases the critical path, a change request need to be created and approved and the schedule rebaselined, otherwise just add the tasks and don't touch the baseline.