How to add changed resources after save and build to development

In most cases, yes... "add all changed resources" is going to get you what you need... this does exactly what it says, it will get all changes and create revisions for them in your build...

However, if you have changes that you don't want included... such as things you are still working on / tweaking; or if you have multiple Dev environments and multiple team members working on changes in isolation... then you might not want to create a build with everything....

In these scenarios, you can do a few things depending on the complexity...

1. You can use the "add all changed resources", then manually remove the items that aren't quite ready to go (if they are new), or manually choose the older revision (this of course can get tricky cause choosing an older revision means building another new revision with the old code... which can be a bit of a build struggle back and forth)
2. If you do have parallel builds, sometimes it is better to just manually select changes and manually build new revisions for the scope of your build... you can do this in two ways:
   1. If the item is already in the scope of your build, but you have changes, select the change from the list and expand it... you should see 4 columns of information (the first being the type), the second being item (both of which are obvious based on what you expanded)... then you will see a list of revisions... here you can choose "Latest", and in the last column, you will see change information and some options, such as "Select Revision" (for existing Revisions), or "Select and Create a New Revision" for versions that don't yet have a built revision... For Latest, you will use "Select and Create a New Revision" to create a new revision for that resource. 
      • If you haven't seen this before, there is also a "Compare Revisions" button that will allow you to do a side by side compare between any two revisions, which will allow you to see what has changed
   2. If the item isn't yet in the scope, but you don't want / or can't use the "Add all changed resources" option, you can manually add new resources to your build using "Add a Resource"... this will allow you to select resources one at a time (this will show the same 4 column display as above (so now you understand why type and item appeared above, it's the same interface), here you can navigate to the resource you want to add, choose a revision, and build it

You can find more information here: https://experienceleague.adobe.com/docs/experience-platform/tags/publish/libraries.html?lang=en

I hope this helps