Yes you can, but that would be a really, really, bad move.
Stick with only one Realtor.
However, don't you think more analysis is needed?
Based on historic sales, what level of activity is expected?
Based on histgoric sales, are you priced within 10% of the value barcket?
Based on historic sales, is the list price reflective of the homes condition?
What has been the result of your agents marketing?
1. How many level one views?
2. How many level two view? (should be 10 times sales)
3. How many showings?
If your agent has accomplished the marketing goal in #2, the agent is not your issue.
The marketing IS WORKING. The buyers are rejectiing your home.
Your agent has already discussed with you what you must do, but you simply don't believe.
This is not uncommon. Very often, sellers are more able to hear the advise of the second agent and make the needed correction.
In response to your question..ONE AGENT AT A TIME.
You are aware that your agent IS marketing your home through other REALTORS, right?