you can use the label_replace function in promQL, but it also add the label, don't replace it

label_replace(
  <vector_expr>, "<desired_label>", "$1", "<existing_label>", "(.+)"
)

label_replace(
node_systemd_unit_state{instance="server-01",job="node-exporters",name="kubelet.service",state="active"},
"unit_name","$1","name", "(.+)"
)

So, to avoid the repetition you can add:

sum(label_replace(
    node_systemd_unit_state{instance="server-01",job="node-exporters",name="kubelet.service",state="active"},
    "unit_name","$1","name", "(.+)"
    )
)by(unit_name)

To change values of the labels you can use same function as to renaming labels: label_replace. For it to change value of the label you need to pass same name into destination and target labels.

For your example query will look like this

label_replace(
  label_replace(
    test_gauge{},
    "name","renamed_value",
    "name","name_value")
  "test_label","renamed_$1",
  "test_label","(.+)")

Here label_replace is applied tow times: one for each label.

Also notice, that here I showed two different approaches:

1. simple replacement of a single value with another value for name. Any metric test_gauge with label name set name_value will have it replaced with renamed_value. But other values of label name wouldn't be changed,
2. addition of the renamed_ to all values of label test_label. Any value of test_label will be modified.

Additionally information:

• please notice, that last parameter for label_replace is a regex, and thus you might need to escape symbols with special meaning in regex before use. For example a[b] -> a\\[b\\]. Notice that escapement is done with two backslashes.
• remember that results of your modifications should result in unique labels sets. For example, you cannot replace label values to same value for all metrics, if that label is the only one for the metric.

You can find a couple demos demonstrating how it works here.

never mind, it was just a question of the regex

label_replace(
    rate(spring_integration_send_seconds_count{result!="success", app="MyApplicationName"}[1m])
     ,"service", 
    "$1", 
    "name",   "(.*).(channel|Channel|handler|ConsumerEndpointFactoryBean).*"
    )