You can negotiate your HELOC rate, just like you can with a conventional mortgage, but you must do your homework. There are numerous companies competing for your business, so you may be able to find more advantageous quotes for a new HELOC deal. These quotes can then be used to negotiate the rate with your current HELOC provider.
However, you should be prepared to switch to a new provider. If your current lender is unable to match the rate on your best offer, you must consider the costs of switching providers before proceeding. For example, it's pointless to save $50 per month if you have to pay $5,000 in early repayment fees and charges.