can a process business rule update a relate field

I have a global account field automatically updating into our accounts module from our ERP as text. I would like to take that text data and update a global account relate field so I could click into a global account and see all of it's related accounts. 

Mapping the global account ID's to the ERP is not an option so I thought a business rule would be a work around. 

Can a business rule update a relate field? 

Example below: I can pull the lookup field but it does not look like I can select the value I want it to return. 

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