Your EASA license is an ICAO license. Most major licenses (EASA, FAA, CASA for example) are all ICAO approved. They want you to have an ICAO approved license so it's easy to convert it to their local license.
Plenty of people have several licenses, side by side, myself included. They are completely separate.
After 3 years (I THINK) your rating will fully expire and be removed from your EASA license. If you're using the type rating under another, new license you can transfer the qualification quickly, but I'm not sure what checks or training are required. If anything, it's way cheaper and quicker than doing a TR again.
EDIT --
SUBPART G — INSTRUMENT RATING — IR
AMC1 FCL.625(c) IR — Validity, revalidation and renewal
RENEWAL OF INSTRUMENT RATING: REFRESHER TRAINING
(a) Paragraph (b)(1) of FCL.740 determines that if the instrument rating has lapsed, the applicant shall go through refresher training at an ATO, to reach the level of proficiency needed to pass the instrument element of the skill test prescribed in Appendix 9 to Part-FCL. The amount of refresher training needed should be determined on a case-by-case basis by the ATO, taking into account the following factors:
(1) the experience of the applicant. To determine this, the ATO should evaluate the pilot’s log book, and, if necessary, conduct a test in an FSTD.
(2) the amount of time lapsed since the expiry of the validity period of the rating. The amount of training needed to reach the desired level of proficiency should increase with the time lapsed. In some cases, after evaluating the pilot, and when the time lapsed is very limited (less than 3 months), the ATO may even determine that no further refresher training is necessary. The following may be taken as guidance when determining the needs of the applicant:
(i) expiry for a period shorter than 3 months: no supplementary requirements;
(ii) expiry for longer than 3 months but shorter than 1 year: a minimum of one training session;
(iii) expiry for longer than 1 year but shorter than 7 years: a minimum of three training sessions;
(iv) expiry for longer than 7 years: the applicant should undergo the full training course for the issue of the IR.
(b) Once the ATO has determined the needs of the applicant, it should develop an individual training programme, which should be based on the initial training for the issue of instrument ratings and focus on the aspects where the applicant has shown the greatest needs.
(c) After successful completion of the training, the ATO should give a certificate to the applicant, to be submitted to the competent authority when applying for the renewal.
Quote:
SUBPART H — CLASS AND TYPE RATINGS
AMC1 FCL.740(b)(1) Validity and renewal of class and type ratings
RENEWAL OF CLASS AND TYPE RATINGS: REFRESHER TRAINING
(a) Paragraph (b)(1) of FCL.740 determines that if a class or type rating has lapsed, the applicant shall take refresher training at an ATO. The objective of the training is to reach the level of proficiency necessary to safely operate the relevant type or class of aircraft. The amount of refresher training needed should be determined on a case-by-case basis by the ATO, taking into account the following factors:
(1) the experience of the applicant. To determine this, the ATO should evaluate the pilot’s log book, and, if necessary, conduct a test in an FSTD;
(2) the complexity of the aircraft;
(3) the amount of time lapsed since the expiry of the validity period of the rating. The amount of training needed to reach the desired level of proficiency should increase with the time lapsed. In some cases, after evaluating the pilot, and when the time lapsed is very limited (less than 3 months), the ATO may even determine that no further refresher training is necessary. When determining the needs of the pilot, the following items can be taken into consideration:
(i) expiry shorter than 3 months: no supplementary requirements;
(ii) expiry longer than 3 months but shorter than 1 year: a minimum of two training sessions;
(iii) expiry longer than 1 year but shorter than 3 years: a minimum of three training sessions in which the most important malfunctions in the available systems are covered;
(iv) expiry longer than 3 years: the applicant should again undergo the training required for the initial issue of the rating or, in case of helicopter, the training required for the ‘additional type issue’, according to other valid ratings held.
(b) Once the ATO has determined the needs of the applicant, it should develop an individual training programme that should be based on the initial training for the issue of the rating and focus on the aspects where the applicant has shown the greatest needs.
(c) After successful completion of the training, the ATO should give a certificate, or other documental evidence that the training has been successfully achieved to the applicant, to be submitted to the competent authority when applying for the renewal. The certificate or documental evidence needs to contain a description of the training programme.