Replace value based on condition from other column

You almost did it. 🙂

= Table.ReplaceValue(
                #"Changed Type",
                each if [PARK_ID] = 88 then [Campground_Name] else false,
                each "Chain Lakes South",
                Replacer.ReplaceValue,
                {"Campground_Name"}
            )

Before:

After:

Full code:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSUQrOz01VyM9JUSguKU1LU4rViVYywi5sjF3YwgK7uKUlCepjAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [PARK_ID = _t, Campground_Name = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"PARK_ID", Int64.Type}, {"Campground_Name", type text}}),
    #"Replaced Value" 
        = Table.ReplaceValue(
                #"Changed Type",
                each if [PARK_ID] = 88 then [Campground_Name] else false,
                each "Chain Lakes South",
                Replacer.ReplaceValue,
                {"Campground_Name"}
            )
in
    #"Replaced Value"