New sleeveless garments and altering my own?

Since the new sleeveless design is posted, but not available until Q4 of this year, is there any reason I cannot alter my own garment tops? I’ve worn garments for 40 years and always always always remember the council to not alter them to suit the “fashion of the day”. However, the new style is published so I’m not making up a design. Also in this way I can use my existing garments instead of buying all new ones when they become available in the US.