[R] How to change all name of variables

[Muhammad Subianto]

Dear R-helpers,
First I apologize if my question is quite simple
I have a large datasets which more 100 variables.
For a research I need to change all name of variables with add one or
more letters on each variables.
For example,
 > data(Pima.tr)
 > Pima.tr[1:5,]
   npreg glu bp skin  bmi   ped age type
1     5  86 68   28 30.2 0.364  24   No
2     7 195 70   33 25.1 0.163  55  Yes
3     5  77 82   41 35.8 0.156  35   No
4     0 165 76   43 47.9 0.259  26   No
5     0 107 60   25 26.4 0.133  23   No
 >
 > dimnames(Pima.tr)[[2]]
[1] "npreg" "glu"   "bp"    "skin"  "bmi"   "ped"   "age"   "type"
 >

I need to change the variables name ,
"npreg" "glu" "bp" "skin" "bmi" "ped" "age" "type"
with
"xyz.npreg" "xyz.glu" "xyz.bp" "xyz.skin" "xyz.bmi" "xyz.ped" "xyz.age" 
"xyz.type"

How can I make this (automatically). I don't want to make manual with 
more 100 variables.
I  would be very happy if anyone could help me.
Thank you for your time.
Kindly regards, Muhammad Subianto