From the incoming processor, is it possible to get the Tempo Java API to get an account and assigning to a custom field:
import com.atlassian.jira.component.ComponentAccessor
def exaPlugin = ComponentAccessor.pluginAccessor.getEnabledPlugin("com.tempoplugin.tempo-accounts")
def exaCl = exaPlugin.getClassLoader()
def essClass = exaCl.loadClass("com.tempoplugin.accounts.account.api.AccountService")
def ess = ComponentAccessor.getOSGiComponentInstanceOfType(essClass)
def projectId = issue.project?.id ?: nodeHelper.getProject(issue.projectKey).id
def allAccountsForProject = ess.getAccountsByProject(projectId).get()
//Other methods: getAccounts(boolean), getAccountId(java.lang.String), getAllAccounts(), getAccountById(int), getAccountByIds(java.util.Set).
//This is an example where the field is set from a default CF
//String accountName = replica.customFields."Account".value
String accountName = "The Account"
issue.customFields."Account".value = allAccountsForProject.find{acc -> acc.name == accountName}