Decrypt values with the same key at different levels from base64 - json

Question

My input is like below. I want to search for SearchString key (you can see that we can't use a fixed index for it) and when the key appears decrypt its value from base64 (perhaps using #base64d filter). Is this possible with JQ? If so, how?
[
{
"Name": "searchblock",
"Priority": 3,
"Statement": {
"RateBasedStatement": {
"Limit": 100,
"AggregateKeyType": "IP",
"ScopeDownStatement": {
"ByteMatchStatement": {
"SearchString": "Y2F0YWxvZ3NlYXJjaA==",
"FieldToMatch": {
"UriPath": {}
},
"TextTransformations": [
{
"Priority": 0,
"Type": "LOWERCASE"
}
],
"PositionalConstraint": "CONTAINS"
}
}
}
},
"Action": {
"Block": {}
},
"VisibilityConfig": {
"SampledRequestsEnabled": true,
"CloudWatchMetricsEnabled": true,
"MetricName": "searchblock"
}
},
{
"Name": "bot-block",
"Priority": 4,
"Statement": {
"ByteMatchStatement": {
"SearchString": "Ym90",
"FieldToMatch": {
"SingleHeader": {
"Name": "user-agent"
}
},
"TextTransformations": [
{
"Priority": 0,
"Type": "LOWERCASE"
}
],
"PositionalConstraint": "CONTAINS"
}
},
"Action": {
"Allow": {}
},
"VisibilityConfig": {
"SampledRequestsEnabled": true,
"CloudWatchMetricsEnabled": true,
"MetricName": "user-agent"
}
}
]

Answer 1

We use path, paths, getpath, and setpath built-ins for such operations when a fixed path is not available.
getpath(paths | select(.[-1] == "SearchString")) |= #base64d
Online demo

Answer 2

walk is quite intuitive for this kind of task:
walk(if type == "object" and .SearchString
then .SearchString |= #base64d else . end)
Using this approach, it's also trivial to modify the program to make it more robust, e.g. to check that .SearchString is a string:
walk(if type == "object" and (.SearchString|type) == "string"
then .SearchString |= #base64d else . end)
Note: if your jq does not include walk, you can simply copy its def from any reputable web site, or from https://github.com/stedolan/jq/blob/master/src/builtin.jq