You don't have to delete lyrics, just comment.
E.g.
{block name='product_reference'} {if isset($product.reference_to_display) && $product.reference_to_display neq ''} <div class="product-reference"> <label class="label">{l s='Reference' d='Shop.Theme.Catalog'} </label> <span itemprop="sku">{$product.reference_to_display}</span> </div> {/if} {/block}
to:
{*block name='product_reference'} {if isset($product.reference_to_display) && $product.reference_to_display neq ''} <div class="product-reference"> <label class="label">{l s='Reference' d='Shop.Theme.Catalog'} </label> <span itemprop="sku">{$product.reference_to_display}</span> </div> {/if} {/block*}
An asterisk is added to the block.