Looks like you would have to do the CTP course even if you have an ATP-SEL.

(b)Airplane category rating with a single-engine class rating. A

person applying for an airline transport certificate with an

airplane category and single-engine class

ratingwho holds an airline transport pilot certificate with another

aircraft category

rating must:

(1) Meet the

eligibility requirements of

§ 61.153 of this part;

(2) Pass a

knowledge test on the aeronautical knowledge areas of

§ 61.155(c) of this part;

(3) Comply with the requirements in

§ 61.157(b) of this part, if appropriate;

(4) Meet the applicable

aeronautical experience requirements of

§ 61.159 of this part; and

(5) Pass the

practical test on the areas of operation of

§ 61.157(e)(1) of this part.

(c)Airplane category rating with a multiengine class rating. A

person applying for an airline transport certificate with an

airplane category and multiengine class

ratingwho holds an airline transport certificate with another

aircraft category

rating must:

(1) Meet the

eligibility requirements of

§ 61.153 of this part;

(2) After July 31, 2014, successfully complete the airline transport pilot certification training program specified in

§ 61.156;

(3) Pass a

knowledge test for an

airplane category multiengine class

rating or type

rating on the aeronautical knowledge areas of

§ 61.155(c);

(4) Comply with the requirements in

§ 61.157(b) of this part, if appropriate;

(5) Meet the

aeronautical experience requirements of

§ 61.159 or

§ 61.160; and

(6) Pass the

practical test on the areas of operation of

§ 61.157(e)(2) of this part.