Keep all INDIVIDUAL kubeconfig.yaml files under .kube/contexts

Then put the following line in your .bashrc (Linux) or .bash_profile (MacOS)

.kube/contexts
├── k8scluster1.yaml
└── k8scluster2.yaml

export KUBECONFIG=${HOME}/.kube/config:$(for YAML in $(find ${HOME}/.kube/contexts -name '*.yaml') ; do echo -n ":${YAML}"; done)