How to set global BitBake variable in one task so that it will be noticable in another task?

Question

I recently started to work with Yocto and now trying to understand how exactly "global" variables of some recipe work. Till now I had a recipe as follows:

# my-recipe.bb
FILES_${PN} += "/lib/mypackage1/package1-shared-object.so"

do_install() {
    install -d ${D}/lib/mypackage1/
    install ${S}/mypackage1/* ${D}/lib/mypackage1/
}

RPROVIDES_${PN} += "package1-shared-object.so"

This works fine - i.e. - the package1-shared-object.so file was installed correctly within the /lib/mypackage1/package1-shared-object.so path of my image.

Now I need to install under the /lib folder some two more shared-objects of two additional packages, so eventually I will have:

/lib/mypackage1/package1-shared-object.so

/lib/mypackage2/package2-shared-object.so

/lib/mypackage3/package3-shared-object.so

The list of mypackages is given to my recipe via the variable MY_RECIPE_PACKAGES_LIST, i.e. - it is: MY_RECIPE_PACKAGES_LIST = "mypackage1 mypackage2 mypackage3"

So now my updated do_install task in my recipe is as follows:

# my-recipe.bb

do_install() {

    // iterate over the list of packages and for each install the respective shared object in the desired location:
    for package_name in ${MY_RECIPE_PACKAGES_LIST}; do
        install -d ${D}/lib/${package_name}
        # the shared-objectX is the only file under: ${S}/package_name/
        cp ${S}/${package_name}/* ${D}/lib/${package_name}
    done
}

The do_install task works fine (I look into the image folder of my-recipe and I see all 3 shared-object's in their desired location).

HOWEVER, when I run the recipe, I get the following error as part of the do_package task.

ERROR: my-recipe do_package: QA Issue: my-recipe: Files/directories were installed but not shipped in any package: /lib/mypackage1/package1-shared-object.so /lib/mypackage2/package2-shared-object.so /lib/mypackage3/package3-shared-object.so Please set FILES such that these items are packaged. Alternatively if they are unneeded, avoid installing them or delete them within do_install. my-recipe: 3 installed and not shipped files. [installed-vs-shipped] ERROR: my-recipe do_package: Fatal QA errors found, failing task.

I looked at the this Q&A: How does the variable scope in BitBake works

and added the python myprefunc to my-recipe so it is now:

# my-recipe.bb

do_install() {

    // iterate over the list of packages and for each install the respective shared object in the desired location:
    for package_name in ${MY_RECIPE_PACKAGES_LIST}; do
        install -d ${D}/lib/${package_name}
        # the shared-objectX is the only file under: ${S}/${package_name}
        install -d ${S}/${package_name}/* ${D}/lib/${package_name}
    done
}

python myprefunc() {
     # for I did it "manually, offcourse iterating here is a better approach.
    files_pn = "/lib/mypackage1/package1-shared-object.so /lib/mypackage2/package2-shared-object.so /lib/mypackage3/package3-shared-object.so"
    d.appendVar("FILES_${PN}", files_pn)
}

do_package[prefuncs] += "myprefunc"

BUT still I get the same error for the do_package task.

The questions are:

1. How can I overcome it ("pass"/ complete successfully the do_package task and the entire recipe)?
2. How do I define the FILES_${PN} in my recipe (if at all) "outside" of any task?
3. What about the RPROVIDES_${PN} - how it should be set and when (in which task)?