Can i merge this resource-based policy by using two condition blocks?

First policy:

This policy grants permissions to all members of your AWS Organizations to use the PutEvents action:

      {
  "Sid": "AllowAllAccountsFromOrgToPutEvents",
  "Effect": "Allow",
  "Principal": "*",
  "Action": "events:PutEvents",
  "Resource": "arn:aws:events:us-east-1:accountID:event-bus/eventbusname",
  "Condition": {
    "StringEquals": {
      "aws:PrincipalOrgID": "OrgID"
    }
  }
}

Second policy

In the second policy, note that, I changed accountID to accountID_1 and accountID_2 to explain the exact purpose of this policy:

  {
  "Sid": "AllowStandardAccountToPutEvents",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::accountID_1:root"
  },
  "Action": "events:PutEvents",
  "Resource": "arn:aws:events:us-east-1:accountID_2:event-bus/eventbusname"
}

This policy grants the account accountID_1 permission to publish events to the specified event bus in the account accountID_2.

Now accountID_1 and accountID_2 can be same, which means that at resource(eventbus) side, all identities are granted PutEvents to this event bus in the same account. In that case, this would not be required and can be removed.

Both of these resource policies serve different purposes, first one grants all member accounts access, while second one grants PutEvents access to a particular account.

Conclusion:

1. If you want to allow only your member accounts PutEvents access then second policy can be removed, but you may have requirement to grant any individual account as well, which is not part of org, then you'd want to keep both. So it all depends on your exact requirement.

2. If you want to allow any specific account which is part of the org or outside of org, but not all member accounts, then keep second one and remove first. To mention again accountID_1 is grantee and accountID_2 is grantor.

3. If you want to allow all your org member accounts not any account specifically, then keep first one and remove second one.

Additionally, look at Event Bus Permissions, which would help you to understand more about these permissions.

Feel free to comment here, if you have additional questions, glad to help.