how to upload params through external script without running as node?

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I am trying to run selected nodes in a gui. I found a way to run nodes with roslaunch.core.Node. But this nodes need specific params and somehow i cannot upload params with rosparam.load(yamlfile) and with roslaunch.core.Param. My Nodes wont start because the configurations are missing. I am trying to run this through a python File without initing it as a rosnode. The main issue is here that i cannot upload the parameters into the parameter server. At startup i check if a roscore is running and start it if its not. But therefore afterwards somehow i cannot upload the parameters. Any Ideas?