Assert a resource conforms to FHIR Profile - hl7-fhir

Question

Want to be able to programmatically declare that a FHIR resource conforms to one or more profiles. Especially want to declare conformance to profiles that don't have any extensions, but only restrictions to the resource such as changing the cardinality of an optional property from 0..1 to 1..1 to make it required or restricting a value set/code system.
Want to be able to associate such an assertion to a Resource when it is created (POST operation) as well as after the fact to an existing resource (PUT operation).
This wiki page: http://wiki.hl7.org/index.php?title=Profile_Validation_Tooling suggests using the Category HTTP header but a particular URL is not specified in the example. “Resources are able to declare that they conform to a profile by being "tagged" with the URI that identifies the profile."
Notional profile URL: http://www.hl7.org/fhir/profiles/patient-restriction-profile.xml
For example let's use a simple Patient Resource:
http://www.hl7.org/fhir/Patient/101
<?xml version="1.0" encoding="UTF-8"?>
<Patient xmlns="http://hl7.org/fhir">
<text>
<status value="generated"/>
<div xmlns="http://www.w3.org/1999/xhtml">
Mr. John Smith
</div>
</text>
<identifier>
<use value="usual"/>
<label value="MRN"/>
<system value="urn:oid:1.2.36.146.595.217.0.1"/>
<value value="12345"/>
</identifier>
<name>
<family value="Smith"/>
<given value="John"/>
</name>
<active value="true"/>
</Patient>
UPDATE:
Apparently to add a profile to an existing resource you use tag operations with a taglist as body of the POST with special _tags url suffix.
POST http://www.hl7.org/fhir/Patient/101/_tags
Content-Type: application/xml+fhir
<taglist xmlns="http://hl7.org/fhir">
<category term="http://www.hl7.org/fhir/profiles/patient-restriction-profile.xml"
label="Test profile" scheme="http://hl7.org/fhir/tag/profile"/>
</taglist>

Answer 1

To mark the resource, you'd use
Category: [new profile url];scheme="http://hl7.org/fhir/tag/profile";label="name for profile"
Guidance is here: http://hl7.org/fhir/extras.html#tag
and here: http://hl7.org/fhir/http.html#tags

Answer 2

When you send a resource to a server (either using POST/PUT to update it or to the validation endpoint), you as the sender include a Category header with contains the claims you make as a sender about to which profiles the sent data (in this case an Observation) complies. So this category header would contain the url of the profile the Observation conforms to (because you say it's organization's A's BloodPressure)
Category: http://www.organA.com/profiles/our-fhir-profile#bloodpressure; scheme="http://hl7.org/fhir/tag/profile"
Now, of course, organB would send its profiles like so:
Category: http://www.organB.com/profiles/measurements#bloodpressure; scheme="http://hl7.org/fhir/tag/profile"
It could well be that some instances of observations (because A and B have agreed on some overlap) conform to both:
Category: http://www.organB.com/profiles/measurements#bloodpressure; scheme="http://hl7.org/fhir/tag/profile", http://www.organB.com/profiles/measurements#bloodpressure; scheme="http://hl7.org/fhir/tag/profile"
In addition, the server itself may periodically run all instances against all profiles it knows about and add additional claims.