Bowing, kneeling, or genuflecting at "and was incarnate by the Holy Ghost, of the Virgin Mary, and was made man" is a Roman Catholic practice from the Medieval & Tridentine eras, and has been mostly ignored in that Communion since Vatican II. There never was a rubric for bodily actions during the recitation of the Nicene Creed in the Books of Common Prayer. We can assume the tradition stayed in the minds of Anglicans after the first BCP came out in 1549 (since it was just what people were used to doing), but from 1559 until the 1850s, this was not practiced. At any rate, it isn't mandated by the BCP - it's a very simple, protestant form of worship.
As far as the Church of England is concerned, current Canons Ecclesiastical (Canon B9 section 2) says: 'They shall give reverent attention in the time of divine service, give due reverence to the name of the Lord Jesus and stand at the Creed and the reading of the Holy Gospel at the Holy Communion. When the Prayers are read and Psalms and canticles are said or sung, they shall have regard to the rubrics of the service and locally established custom in the matter of posture, whether of standing, kneeling or sitting.' I use a nod of the head as reverence to the name of Jesus during services. As to other gestures, the 1549 BCP has this to say: “As touching kneeling, crossing, holding up of hands, knocking upon the breast, and other gestures, they may be used or left as every man's devotion serveth without blame.” One may make reverence in the Nicene Creed as Consular has already mentioned at 'and was incarnate by the Holy Ghost of the Virgin Mary, and was made man'. At the end of the Creed one may make the sign of the cross at 'And I look for the resurrection of the dead, and the life of the world to come.' Other occasions during Holy Communion for making the sign of the cross may be: at 'In the name of the Father' etc at the absolution. at the end of the Gloria in Excelsis Deo (Glory be to God on high) sign at 'art most High in the glory of God the Father.' at the announcement of the Holy Gospel. at the Benedictus 'Blessed is he who comes in the name of the Lord.' at the consecration of the bread and wine. (once for each kind). immediately before receiving. (once for each kind). at the blessing. I never genuflect but prefer to bow. (According to Dearmer, aka the Blessed Percy, it was not really an English custom to genuflect before the Reformation, Sarum custom was apparently a profound bow). In the Choir Offices (Morning/Evening Prayer) one may bow at the Gloria Patri at the end of Psalms and Canticles, 'Glory be to the Father' etc and straighten up at 'as it was in the beginning, is now and ever shall be' etc. The sign of the cross may be made at: the opening of the Benedictus, 'Blessed be the Lord God of Israel'. the opening of the Magnificat, 'My soul doth magnify the Lord'. the opening of the Nunc dimittis, 'Lord, now lettest thou thy servant depart in peace'. at the end of the Apostle's Creed, ' the resurrection of the body and the life everlasting'. Other customs include bowing towards the Altar when entering and leaving church and turning East at the Gloria Patri and Creed. There are probably other instances that I've forgotten to mention but in the CofE non are requirements apart from that mentioned in Canon B9. The other examples that I've given are down to individual conscience and churchmanship and also vary from place to place. They are pious customs and not requirements.
Right now we are using the Book of Alternative Services, but as soon as ACNA releases their provincial prayer book I think our priest will use that. It will now say "And with your spirit" instead of the ICEL "And also with you"
That 1973 ICEL response was one of the worst things ever done to the Liturgy... what a silly rendering of "Et cum spiritu tuo"!