Get the element, and set its attribute:

my ($node) = $doc->findnodes('//remote[@name="korg"]');
$node->setAttribute(name => 'other');
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Or get the attribute, and change its value:

my ($node) = $doc->findnodes('//remote/@name[.="korg"]');
$node->setValue('other');
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Three key concepts:

• Everything in the tree is a node, including attributes.
• The square brackets are like a WHERE clause in SQL. The filter which nodes to return.
• "." refers to the topic node. In square brackets, that's the node being tested by the square brackets.