catkin build ONLY the message target of a package

edit

I have packages as follows:

package_A/
|-- msg/
    |-- CustomMsg.msg
    \-- ... (other messages)
|-- include/ ... (some code)
|-- src/ ... (some Python and C++ code)

package_B/ ... (also depends on package_A/CustomMsg.msg)

my_msgs/
|-- msg/ ... (some messages; one depends on package_A/CustomMsg.msg)
\-- ... (srv and action definitions that depend on msg)

my_package_1/ ... (depends on my_msgs)

my_package_2/ ... (depends on my_msgs)

I'm working in Melodic and I have some bag data, pkl files, etc., but unfortunately, I need to work with that data in another distro where it's infeasible for me to setup my workspace again (package_A and package_B won't build because of various dependencies, for example). The way I see it, I have 2 options:

Option 1:

I only need the messages built to work with my data, but I cannot figure out a way to get catkin to only build the message targets and ignore the code that comes in package_A. Is there a way to do this?

CMake doesn't come naturally to me, so when trying to build catkin build package_A_generate_messages failed, I decided to come here for help. If there is a way to build just CustomMsg.msg, even better!

Option 2:

I know that you can work across distros if the message hashes remain unchanged. But I don't know how those hashes are generated. Is the package name taken into account? I think the answer is yes, but wanted to check what else might be. CustomMsg.msg actually has a pretty simple message definition, so if I redefine the message in my own (faux) package called package_A on the other machine and build, will I end up with the same hash, which will then allow me to reuse my data files?