See below, From LASORS. It seems to depend how many hours you have when converting from FAA to JAA PPL. Bear in mind no flight school will let you sit the skills test without being sure you can fly all the JAA maneuvers well enough to pass, this includes the JAA 'way' of navigating, which differs slightly from the FAA method that is generally taught. And the radio phraseology differences too.
The holder of a current and valid PPL(H)* issued
by an ICAO Contracting State (not being a JAA
Member State), who has flown a minimum of 100
hours and meets the JAR-FCL PPL(H) flying
experience requirements (including 5 hours
instrument instruction) as pilot of helicopters, is
credited the JAR-FCL PPL(H) training
requirements, however they will be required to
undertake the PPL(H) Skill Test on a helicopter
type for which he is qualified. Applicants wishing
to take the PPL(H) Skill Test on a helicopter type
on which they are not qualified will be required to
complete the training requirements for an
additional helicopter type as detailed in Section
F8.
• The holder of a current and valid PPL(H)* issued
by an ICAO Contracting State (not being a JAA
Member State), who has flown less than 100
hours as pilot of helicopters, but meets the
JAR-FCL PPL(H) flying experience requirements
(including 5 hours instrument instruction) is
credited the flying training, except the PPL(H)
Skill Test. Applicants wishing to take the PPL(H)
Skill Test on a helicopter type on which they are
not qualified will be required to complete the
training requirements for an additional helicopter
type as detailed in Section F8.
* If the ICAO licence has expired and/or no valid
helicopter rating has been held for a period exceeding
5 years preceding application, applicants will be
required to complete flying training at the discretion of
the Head of Training of the approved training provider,
and pass the PPL(H) Skill Test.
FULL DETAILS OF THE EXPERIENCE/TRAINING
REQUIREMENTS ARE GIVEN IN JAR-FCL 2
SUBPART C
The holder of a current and valid PPL(H)* issued
by an ICAO Contracting State (not being a JAA
Member State), who has flown a minimum of 100
hours as pilot of helicopters, will be required to
pass written examinations in Air Law and Human
Performance and Limitations. (If no helicopter
rating has been held in the 5 years preceding
application, then all JAR theoretical knowledge
examinations would need to be passed. An
applicant who also wishes to obtain a FRTOL will
be required to pass the JAR-FCL PPL
Communications (PPL) theoretical knowledge
examination and practical communications test
unless they qualify for credit as detailed in
Section B1.4.
*If the ICAO PPL(H) has expired then all JAR
theoretical knowledge exams would need to be
passed.
• The holder of a current and valid PPL(H) issued
by an ICAO Contracting State (not being a JAA
Member State), who has flown less than the
minimum of 100 hours as pilot of helicopters, will
be required to pass all JAR theoretical knowledge
examinations.