How to Add to Vagrant Settings From Loaded Vagrantfile - ruby

Question

This may actually be a basic Ruby question more than a Vagrant-specific question. I have two Vagrantfiles. One makes a number of generic settings. The second one makes more specific settings for the particular instance. The first is loaded into the second. The idea is to keep common settings that are the same across all Vagrantfiles in one place so it's normalizes and I don't repeat myself. Some Vagrant settings are an array of strings. If I set one of these in the first Vagrantfile, and I try to add an element to it in the second file, I get an error:
Message: NoMethodError: undefined method `<<' for :__UNSET__VALUE__:Symbol
How can I add to an array?
Here is a boiled down first Vagrantfile with just what I'm interested in:
Vagrantfile.general
# -*- mode: ruby -*-
# vi: set ft=ruby :
Vagrant.configure('2') do |config|
config.vm.provider 'cloud_service' do |cs|
cs.tags = ['ExampleTag1']
end
end
Vagrantfile (Specific)
load 'Vagrantfile.general'
Vagrant.configure('2') do |config|
config.vm.provider 'cloud_service' do |cs|
cs.tags << 'ExampleTag2'
end
end
The following works, but I want to know how to add to the previous array rather than overriding the whole array.
Vagrantfile (Workaround)
load 'Vagrantfile.general'
Vagrant.configure('2') do |config|
config.vm.provider 'cloud_service' do |cs|
cs.tags = ['ExampleTag1', 'ExampleTag2']
end
end
Note: I understand that the tags can be kept in a YAML file that is loaded by first and second files and then added to or subtracted from before setting the tags in the provider. I have read this answer elsewhere. What I am seeking is a more elegant way to handle this. Basically I want to know if it is possible to access the object created by the first Vagrantfile where the array is located and add to it programmatically in the second Vagrantfile using Ruby code.
Update
Here is one option that is Ruby code, but does not access the array inside the Vagrant object: set a global variable in the first Vagrantfile. I'd still like to see an answer that accesses the Vagrant config object and modifies the array.
First
# -*- mode: ruby -*-
# vi: set ft=ruby :
$cs_tags = ['ExampleTag1']
Vagrant.configure('2') do |config|
config.vm.provider 'cloud_service' do |cs|
cs.tags = $cs_tags
end
end
Second
load 'Vagrantfile.general'
$cs_tags << 'ExampleTag2'
Vagrant.configure('2') do |config|
config.vm.provider 'cloud_service' do |cs|
cs.tags = $cs_tags
end
end